I've done a few of these, and in all cases the problem with the shuttle switch assembly contacts was entirely down to corrosion on the PCB pins and the receptacle sockets being loose.
It's a bit fiddly but you can get a fine scriber point down the split sides of the contact sockets and make them tighter. If they are corroded then a piece of 1200 wet & dry dipped in WD-40 and rolled up small will clean them out, but don't go over the top.
The pins should be bright and shiny, not dull.
I've been lucky, no sensor or bearing issues, but with 164K on the clock that's going to happen sometime soon.
Peter