Okay, guys, I've got to weigh in on this one! The oldest loco still in service which I bought new was also my first HO loco, a Tyco Shifter from 1965 or 66. I must have saved my 25-cent-a-week allowance and birthday money for what felt like a year to buy it. Well, a few years ago, it got dismantled and overhauled. It now sports a Sagami motor, and the Cal-Scale brass on it cost more than the original loco. I ground off all the old detail and re-piped it. After a year or two of running, the original tender trucks wore out. The journal bearings wore into vertical slots! I now have a set of Precision Scale Co. tender trucks waiting to get the old girl up and running again!
But, then there is the matter of rolling stock. My dad was in the hobby briefly in 52-53 or so. In 1965, he gave me about 15 of his very meticulously built freight cars. So, I have metal Athearn, Varney, and Main Line cars now equipped with Kadee couplers and trucks--love those old kits! --Stu--