I have been repairing electronics/mechanical assemblies for over 25 years and i have developed the following philosophy.
"If a modification is required to fix a problem, then it is not a fix but a design change and that does not end in a quality result." That is my repair philosophy in one line, with that being said engineers are not perfect and defiantly do make mistakes. Those mistakes can become big problems and are well known. For instance we can point to gottllieb system 1 for example of a bad design that requires modification to keep it running, mainly adding grounds to keep the poor grounding choices of the engineers from constantly failing. But also this failing is well known. Down through the years in my repair career engineering departments quite often issue design changes to repair technicians to correct a flaw in the design.
Modification to repair something is not a good choice when you are in a normal repair situation. One Common modification i see is that if you have a bad connector, then solder the wire and bypass the connector. All you are doing is to frustrate the next repair that will need to be made to keep these antiques running well.
If you are making a modification then understand that you are altering the function. For instance on older em pinball machines you need to modify the credit reel to make the game free play, because there is no free play option on all em machines.
So when you are working on your game, ask yourself the following question "am i repairing it or modifying it" Then if you are modifying it, do you understand the ramifications of the modification. This philosophy is not limited to just the electronics or electrical system, this is also true for the playfield and mechanical assemblies. in fact i see more modifications to the mechanical assemblies then electrical. one mechanical alteration i see allot is shorting a spring to repair not modify the function. The common misconception is that the spring is weak. As a general rule this is not true. In most cases it is a mechanical failure that goes undetected by the person repairing the machine. Just because a lever is moving does not mean that it is moving correctly per the design. Just putting oil on a lever that was designed to run dry does not fix the function of that lever it may work better in the short run but it will eventually cause more problems in the future.