You might want to check your transformer has a circuit breaker(and is working well). Any train that runs is a good one. It is not a rare train, so how(if) you repair it is really up to you. If it runs, I would re-stake it, attempt a screw(s), or use JB-weld as glue. Those weren't always quiet motors. The noise problem could just be lack of lube. And a lose roller might have been causing the some heat with poor contact and caused the derailment. "Jumping" power to the loco and checking smoothness, or loseness may help you figure that out. I think the rollers on that one, are on the motorized truck. The same style(look) of non powered "dummy truck" was made with rollers, and put on other year switchers(they had no rollers on the power truck). A swap, and you could move rollers off the motor you have.
Most PW through modern style switcher chassis/trucks could replace yours, if you want to keep the DT&I shell around. E unit placement might have to be dealt with. Williams by Bachmann NW parts could likely be used as replacements with a modern drive. I think they are essentially modern but near identical copies. A checking with a company called Timco (Frank(?)) for a modern replacement is another option (use OGF search for more info. He is an OGF member too I beleive)
