Lose one of those tiny bearings in disassembly of your ace pro unit and can't find it? Don't worry, you're not alone. Here's a somewhat temporary but possibly permanent solution to losing one. You should replace it if you can, but this has been working for me without issues for days now. I printed with high temp pla, but petg or abs might be a better idea.

Bearing is 7mm x 3mm with a 3.2mm gap in the middle. Press fits onto the metal rod perfectly and snaps into the holder in the ace pro.