I picked up a set of N scale stuff on Saturday that included 3 locomotives. One of the steam engines gears/wheels dont want to turn and when I took it's cap off, it has that worm gear which also doesnt always turn when the wheels are put to the track. Another one i have, diesel, "works" but it's very jumpy and loud. maybe just needs oil? Any tips on cleaning/maintenance of N scale locos? The HO scale ones I have dont seem to have as many visible gears on them so i'm a little leery of taking these N scale apart. Thanks in advance.