Final Update - I tried everything I could think of, including pulling both wheels off the drive axle, put them back on using Loctite 271, squared everything up, but it was all for naught - the brass tube axle is bent. Fortunately, Lionel had a new drive axle, complete with worm gear and green Percy drive wheels, so I bought one, put it in, and it now runs smooth as silk. Conclusion: the axle was bent, and when that happens to a brass tube axle, that's the end of it (for me.) It was not worth the effort, but I was doing it to learn, so I have now learned not to do that again! 
Glad to have Percy added back to the livery
One last FYI, the new drive axle's magnetraction is identical to the old one. It appears they put only one tiny little itty-bitty magnet in the new axle (same as the old one) and it sucked over to the right wheel, and that wheel has the tiniest bit of magnetism, while the other wheel has none. What a plan that was!!!
