It looks as if you've found the reason that it doesn't run. :thumb: It's probably a good thing that I wasn't here to answer your post of 9:56, as I would've told you that the reason that the gears were turning freely was because the gear boxes had dropped slightly when you removed the bottom covers. If the screws were long enough to reach when you had put the covers back in place, tightening them would've drawn the gearboxes back into their proper positions. This worked out even better, though, as that piece of tubing appears to be the culprit. The best choice to replace it is model airplane fuel line - get a foot or so of it and cut a piece to fit. You'll want tubing that's a tight fit on the shafts, and flexible too. On the shaft between the two gearboxes, ensure that the screws that hold the female parts of the universal joints in place are tight. While you've got it apart, open up those gear boxes and check the lubricant. If it's hardened or not present, note which way everything fits together, then disassemble it and clean the gears and inside of the cases. A toothbrush and some mineral spirits will work or the brush and some dish detergent and warm water. Do one gearbox at a time, and dry the parts thoroughly before re-assembly. Lube the gear teeth and the shafts on which they turn, and the worms and their bearings. NWSL recommends LaBelle #102 Gear Oil for this purpose. I was surprised to see in your earlier picture that the driver gears appear to be steel, as the best practice is to have the driven gear of a softer material than the drive gear. However, the gearboxes clearly contain an idler gear, which is undoubtedly brass, while the worm will be, correctly, steel. This means that the gear made from the softest material, the brass idler, is the most likely to wear out first, but also the easiest to replace - good engineering. :thumb:
As I indicated earlier, apply just a tiny drop of oil where the shafts enter the motor, too, preferably at both ends.
While you've got the engines free from the drive train, place each on a sheet of glass and see how well they'll roll when given a light push. The rear one may bind, as the piston and main rod don't have the cylinder to keep things properly aligned. If you haven't already done so, apply a drop of oil on the inside face of the driver bearings, right at the point where the axle passes through: a couple turns of the wheels will draw it in to where it will do some good. This is easiest to do from above, as can be seen in your photo of the rear engine, but it is also possible to do from below if the loco is not disassembled. I mention this only to remind you that you'll need to do this periodically - just a drop is sufficient.
There are many causes of binds in the siderods and valve gear, and often the best way to discover them is to run the loco slowly, upside down, on the bench while observing carefully. Common problem areas are the rear face of a siderod contacting the front face of another, or contacting protruding driver counterweights. These cases usually make an audible "click" as the parts come in contact. The solution to this type of bind is spacer washers installed to increase the clearance between moving parts. If the valve gear binds in this manner, the easiest cure is to gently bend the offending parts to remove the interference. I normally oil all of the bearing surfaces of the valve gear and siderods after painting: oiling before will allow a small amount of oil to spread over areas that are to be painted, resulting in poor paint adhesion. Depending on the preference of the painter, he'll likely clean all of this area before painting, anyway: I generally disassemble the loco as much as necessary for painting, remove the motor, then throw the whole shebang into a sinkful of hot, soapy water (which means everything will need to be re-lubed anyway).
At least you've discovered the major reason for the loco not running and found that it's a cheap and easy fix: an unscrupulous painter could've charged you for a much more complicated and expensive (but unnecessary) repair. Plus, you've gained some valuable experience and useful knowledge just by having the courage to take screwdriver in hand to "have a look". My compliments to you, Chris, for doing so.
Wayne
As I indicated earlier, apply just a tiny drop of oil where the shafts enter the motor, too, preferably at both ends.
While you've got the engines free from the drive train, place each on a sheet of glass and see how well they'll roll when given a light push. The rear one may bind, as the piston and main rod don't have the cylinder to keep things properly aligned. If you haven't already done so, apply a drop of oil on the inside face of the driver bearings, right at the point where the axle passes through: a couple turns of the wheels will draw it in to where it will do some good. This is easiest to do from above, as can be seen in your photo of the rear engine, but it is also possible to do from below if the loco is not disassembled. I mention this only to remind you that you'll need to do this periodically - just a drop is sufficient.
There are many causes of binds in the siderods and valve gear, and often the best way to discover them is to run the loco slowly, upside down, on the bench while observing carefully. Common problem areas are the rear face of a siderod contacting the front face of another, or contacting protruding driver counterweights. These cases usually make an audible "click" as the parts come in contact. The solution to this type of bind is spacer washers installed to increase the clearance between moving parts. If the valve gear binds in this manner, the easiest cure is to gently bend the offending parts to remove the interference. I normally oil all of the bearing surfaces of the valve gear and siderods after painting: oiling before will allow a small amount of oil to spread over areas that are to be painted, resulting in poor paint adhesion. Depending on the preference of the painter, he'll likely clean all of this area before painting, anyway: I generally disassemble the loco as much as necessary for painting, remove the motor, then throw the whole shebang into a sinkful of hot, soapy water (which means everything will need to be re-lubed anyway).

At least you've discovered the major reason for the loco not running and found that it's a cheap and easy fix: an unscrupulous painter could've charged you for a much more complicated and expensive (but unnecessary) repair. Plus, you've gained some valuable experience and useful knowledge just by having the courage to take screwdriver in hand to "have a look". My compliments to you, Chris, for doing so.
Wayne