Sonic/Segasa is a Williams clone and pretty much anything inside can be replaced by Williams bits. Gotta love those armor plated playfields too. Zaccaria EM innards look like Williams stuff as well. These aren't terribly difficult to keep working.
I have a Recel Top Speed - some of the pieces look like Gottlieb machinery and others look like they went their own way. Some creativity may be needed by whomever gets to rebuild the flippers on that one.
PBR has some off-brand coils listed and weird foreign stuff shows up on flebay every once in a while.
Parts can be modified - grind 1/8" off a Bally plunger to make it fit someplace they never intended. Parts can be substituted - everybody's pop bumpers get rebuilt with Gottlieb bits nowadays.
Some games are indeed more difficult to refurb due to unobtanium parts. Here's a nice example - some drop target links for DynO'Mite that I whittled out of a hunk of plastic.
oops... Allied Leisure wasn't an overseas manufacturer.