Below is a "do it yourself" video showing some of his work. He charged $80 (+shipping) to replace the diode and the subwoofer.
Now I just have them paired via Airplay 2, so they are no longer stereo. Not really a big deal for their current implementation, but if I want to move them to a bedroom in the future, I could use them rather than setting up a receiver with speakers. Actually, this is something I am currently thinking about with updates we plan to make down the road. Right now, I have full size speakers in the bedroom that we like, but the setup takes up a ton of space. Mounting these next to a wall mounted TV would be pretty awesome and would definitely get a lot more use than my current speakers.
Anyway, if you want someone to fix an old HomePod, Nic got mine fixed and back in my hands inside a week.