Comment by namuol
Yeah the buttons are actually tactile switches - it was hard to find ones that fit but eventually I found a good match on Ali express. You want 4.8x4.8x0.55mm smd thin film tactile switches. [1]
Only one button was malfunctioning but I replaced them all since they looked pretty worn.
If you’re thinking of switching to micro usb you might as well try usb-c. AFAIK you’ll still need to deal with alignment issues. The resistors are only necessary if you want to use modern PD chargers - they make little boards with these attached already but it may be impossible to fit one of those.
Probably worth posting your work somewhere, I feel like there's probably a subreddit or two that would be interested (maybe the Rockbox forum too?).
Could definitely make a decent markup buying broken ones and reselling them all fixed up too; I got seven "broken" ones a few months ago on eBay for $20 and almost all of them just had dead batteries