I love playing tournaments, I like playing in my basement, I'm okay with cleaning the machine - but I hat repairing so much.
If there is something I can make worse if I do anything more than adjusting the flippers, I'll do 95% of the time.

I am so happy I found somebody who can help me with this stuff, for a compensation I can live with.
And that's my advice find somebody, make a list of your issues and then do a repair session once in a while.
It's not helpful to fix everything at once, collect the issues - especially if you more than five machines, which is in general a blessing.

Here is my experience... risking some downvotes

JJP mostly out of the box issues, sometimes not so easy to fix. After the initial work rarely problems.
Stern rarely out of the box issues, very rarely later
WPC depending on what you have bought... perfect "out of the box" or a complete desaster. Issues can relatively easy handled since all spareparts are available for a reasonable price und there is a lot of expreience out there repairing these machines
Early solid states (Bally only)... more or less same like WPC... maybe even more convenient
EMs... you should be an expert by your own... repair jobs are often very time comsuming - the main reason I don't have them anymore even though I love playing a good EM

In general switches, contact, coils, etc. were used a lot (million and million times) on pre 2000 machines, maybe even on whitestars oder sams so they will break one after another. Newer Sterns oder JJPs don't have this type of problem so once they are dialed in you are pretty safe.