Dave,
Welcome to the Forum!
I have a 1946 ~ Lionel 221 & 221W tender, so I  am familiar with some of it's quirks.

It sounds as if the roller pickup on the locomotive may be bent down too far and catching on the activator of the
uncoupling track as it passes over, causing the loco to jump/derail.
or
The actuator on the uncoupling track may be bent up enough to catch the roller pickup on the loco as it passes over.

If you have another uncoupling track, try replacing the  piece that you're having issues with and see it the loco still jumps/derails there. 

If that doesn't do the trick, then check the pickup roller.

Dave

Dave,
I just checked mine & it has the slider shoes also.
You can check to make sure the springs are operating correctly, the shoes should slide up and down easily.
Check to make sure that the shoe hasn't been bent out of shape on the leading edge and make sure that the lip of the following(2nd) slider shoe points up so it will slide over the uncoupler actuator.

Dave

Dave,
The 1946 ~ 221's were painted Grey, the 1947 ~ 221's were painted Black.

As to repainting your locomotive and tender I'm sure that the paint can be matched if it is not available commercially.

Personally, I don't believe in repainting  unless the original paint is totally wasted.  When you repaint, you destroy the history, love & play the train has received over the years, taking away the originality & individual personality  the locomotive has developed over its lifetime.

So, unless it's a total piece of junk paintwise, I'd just clean it up really well and apply a coat of wax to it.

Dave