A very early locomotive to my collection, I was too scared to take it off the shelf because it might fall apart. The brushes are almost paper thin, the tires on 2 driving wheels and one of the trailing trucks has fallen off. One day I am going to remotor it and get some new wheels. Believe it or not, this thing STILL RUNS.
Not at home but we have a few at the club, where locos get a lot of running time. We have a Kato SD40 that has worn trucks (the frames that hold the wheels). Power pickup suffers from that. Probably results from lack of lubrication. Of course, the hand rails are broken. Other locos have worn wheels, etc.
That engine is fairly common on eBay. I would suggest that you buy another one that is in good mechanical shape and put your old boiler shell on it so it’s still visually the same locomotive. And keep the old mechanism for parts as you may need them from time to time.
For years now, Individual parts to repair locomotives have not been available for anything. You have to buy a new donor engine to either get the parts or substitute the mechanism. I suggest substituting the mechanism, to get one that already runs trouble free. You can then put the second boiler on the old frame and get yourself a display piece again.
I don’t get to run my layout as much as I’d like . Plus, I have a good many engines to spread the running time out between. The end result that I don’t have anything that really wears out. But I did have a couple of engines that in the past had ill advised repairs done to them to the point that I had to replace the messed up mechanisms. Those engines received heart transplants in the form of new donor mechanisms, with the original shell put back on them so they still look like my engines from the days of yore. But they now run trouble free like the youngsters that they mechanically are now.
The problem is that even when I had it brand new it did not have good low speed and it wobbled a little while running. It also was just about my worst pulling locomotive out of some old Bachmanns and a few Life-Like pieces
Well, then, maybe it’s best function is as a sentimental display piece.
That engine is a USRA pacific. Better running HO models of that engine have been made. Bachmann is still offering that engine in several road names. Broadway Limited did for a while and those may be available on eBay. It sounds like if you do heart surgery on this it won’t be that good of a running engine anyway, I’d get a better model if that’s the engine I want.