One time a 5890 round oven-vent cover broke free from the motor-actuated rod; I went home at lunch time and fixed that by installing a couple of rivets.
I've rebuilt a few of those. For a while I seemed to have a rash of flappers going bad in various ways, and just started swapping them as needed and rebuilding as I had the time(although IIRC-it's been a few years since I've messed with one) the 5890 flapper motor goes into an 8 or so pin Molex-type plug and you need a pin extractor to pull it loose.
The flaps themselves always made me happy at least as fixes go. I got to where, once I had the assembly out, I could do one in ~10 minutes by just drilling out the arm, flap, and the metal backing plate(and anything else in the "sandwich" if I've forgotten something) and pop riveting it all back together. I never had a repair one fail, and I started proactively just doing both after once or twice of one of the flaps failing and then the other going a few weeks later.
I still have one or two with a faulty coupling between the motor and the arm. They could probably be fixed-I forget the exact mode of failure but know that basically the arm swings free from the flap. I'd thought of cross drilling and pinning, especially as the motor itself still worked, but never had the need to go that route as I still have a few good ones salvaged from 5890s we ended up parting/junking out.
I'm pretty sure the oven flapper was the only mechanical part I've ever actually had issues with on the 5890. I have a couple of oven fan motors and other odds and ends I've saved, but don't recall ever having to replace one...on the whole HP built a pretty darn good basic chassis in the 5890, and I guess the fact that even the 8890 feels very familiar to someone who has worked inside a 5890 shows that.