Once you're familiar with the typical problem areas, they aren't as bad to work on as people say. Address those issues, and they're solid as any other machine.
Williams, Bally, Stern--all those games have their quirks and issues. Gottlieb is no different.
The board interconnect, special solenoids, and overloaded GI on classic Williams? Ugh. How about the awful chip sockets, connectors, and burnt/hacked up rectifier boards on classic Bally/Stern? Double ugh.
I can usually get a System 80 game up and flipping much more quickly than classic Williams/Bally/Stern games. It usually seems like there's a lot less effort involved.
However, yes, there are certain chips that are difficult to get--especially when it comes to sound boards. But that's fairly typical since sound technology advanced so quickly and changed so much. Try finding some of the sound chips for the Stern VSU-100 speech board or the Bally S&T board--some of those are nearly impossible to get.
System 80 games really aren't any worse than any other game system. Heck, System 1 games aren't even that bad either once you address the common problem areas. Everybody just seems to panic when faced with a Gottlieb game just because it's a little different than what they're used to compared to classic Williams/Bally/Stern. They really aren't that scary to work on.