Rubber bands tied together to replace the 5 inch rubber on a WMS Flash.
Wood screws used to fix a coil stop in a Bally KISS
A nail soldered on to the casing of a fuse on a Bally Paragon
A piece of plastic glued on to a broken plastic bat on a GTB EM (I can't recall the title)
A Separate arcade style power supply mounted in the lower cabinet of a DMD (can't recall the title) supplying +5 Volts and hacked into the wiring loom.

That was years ago !

But what REALLY is dodgy these days are the amount of route pins that are filthy and not serviced. VERY rare to find a fully working machine. Operators don't care anymore - in the old days, they did everything they could to keep the game going, these days, they do absolutely nothing.