After I had this problem on 2 straight games, I have been moving the spring washer on every new stern I get to the non-coil stop side where it should be. That doesn't mean that the coil stops they use aren't bad, but I also have not had to replace one since. It's rather annoying to have to do this for every flipper mech on a new game. I wish they would just assemble them the right way from the factory. And yes, I have told them about it.

Pinball Life for sure. There may be others.

I'm not convinced they are necessary either but as stevevt mentioned, they may be there to tone down the flipper buzz. The problem with putting them on the coil stop end is it makes plunger/coil stop contact less stable. I learned this years ago on the old Bally linear flipper mechs from the 80's where it caused the flipper mechs to get sluggish and not work quite as well after a while and in some cases blow out coil stops when I put them on the wrong end.

They've been building them this way for many years, so maybe they have been doing it this way from whenever they started adding them. I don't recall seeing them in the older stern titles from the prior decade, but those were also the ones that had flipper buzz.

I make this exact change on every flipper mech of every new Stern I put out on location. It's extra work and it's frustrating that they refuse to put it on the correct way from the factory even though they have been given that feedback. The faulty coil stops might last a little longer, but it doesn't keep them from failing. My other big annoyance is the stupid nub to nub design of the lockbar action button which makes it prone to jamming frequently. Crickets on that one too.