[Cliffradical]

Yeah, the pass-through (ambi) styles are hinged on a 'half moon' kind of crossbar interaction with the selector lever/ selector plate, whereas the older SEF style is just pinned or screwed right into the selector lever more like most ARs, allowing for near direct input between selector lever and selector plate.

Ambi selectors are always going to be subject to more wear and tear. The best systems are hilariously the newer (middle-aged now) CYMA (maybe this is a direct copy of a better brand I don't know about?) types which are one big offset circle as opposed to the older CA (TM origin?) stepped cam style which is most often found on SEF selector groups.

Ultimately, it's a metal on plastic issue, and a failing of V2 AEG MP5 designs, so I try to be gentle and deliberate with my MP5 selectors. Very lightly and carefully lubricating the entire selector group helps over time.
I have an old CYMA SD6 (crossbar/ambi, offset circular, captive detent), and while the body is rattling itself apart the selector is good to go.

Edit: I've also never used the 'Auto' setting outside of funtime mag dumps, and I'm as careful as I can be about what stage of the piston cycle my guns are in when I use my selector, so my selector group has really only had to deal with ~2mms of travel. That helps.