I'm pretty sure the shaft stays with the motor. The bearing rides on the shaft.
So far, just about every machine DH has dealt with has needed to have hardened grease/oil softened and cleaned out of there. Even in the older singer manuals, they state that a machine that has sat for a while will need to have the hardened oil softened and cleaned up before use.
Most of the problem with things not working is due to the hardened grease getting in the way. So that is why a lot of tri-flow works - it dissolves the old grease, but it make take many applications before it's all cleaned. That is also normal with sewing machines - if something is still sticking, assume you didn't get all the old gunk cleaned out yet.
This is really a problem with the 6000 series Viking machines. They were built with a "never lube" grease/oil and it only lasted about 25-30 years, and that it turns into a really hard, glue like substance. And since they not all metal, gears and knobs get broke as someone tries to force them to move when they are stuck.
Compared to them, the 401 is a walk in the park to work on. It may be more complicated than something like a 15 or 66, but by far it's not a hard machine to work on.