About Gottliebs...
From my point of view...( I was operator and tech from 1980 to 2000 ), in my county (Dalmacia)
Gottliebs ARE dominating machines (there IS reason for that, but it is "another" story )

We are talking about reliability... I have seen a LOT of SYS 1 machines which made OVER 100k
games, and few of them over 200k games !!
Some of them was in very, very bad condition ( dirty and worn playfield, missed GI or "half"
controlled lamps, weak fliper(s) , terrible rubbers and coin door with concave "look" )

Reason ?!? ...simplicity of electronic circuits and robustness of mechanical parts,
ESPECIALLY flipper sys

YES...it's also a "lot" of weird details, like ground lines, connectors and obsolete CPU stuff,
but with proper maintenance Gottlieb SYS1 is "indestructible" !!!

With only one IMPORTANT rule - don't pull up a playfield with power on !!!!

I had many pins on service with same story...
" It worked fine, and I have to made some "minor" works UNDER playfield ! " )

SYS 80 (A &B )is similar story with more connectors (ground) problems and
solenoid "baking" problems )

Common conclusion for that era Gottliebs ... with some (quality done !! ) works (and mods
those machines CAN BE extremely reliable !!

Greetings from Croatia )

edit:
UPSSS... I made some offtopic, this is DMD story...ok, I have significantly less experience with
SYS 3 , but there is same (Hamurabi ? ) "law"....

DON'T do "anything" with power ON !!