Quoted from SealClubber:
take mine apart and look at the plunger and coil stop. If there is any mushrooming then I rebuild them. If you do a rebuild, don't forget to replace the playfield bushing too as they are not in the kits.
It's amazing that only the DE/sega early kits have bushings, yet all come with new EOS.
As soon as I get a game. Always replace bushing and sleeve. If the plunger doesn't even remotely look new (tapered slightly at the end), I replace at least that and the link. If the coil *stop* (edit) is even slightly ill formed, replace that too. I will see if the spring, either type, looks good as well.
I keep all used parts for fixer uppers down the road, and for extra parts in a pinch, or to give to my other pinball friends at Christmas.
If it is a high end game, I don't even think twice, I replace the pawl/plunger, sleeve, bushing, bat, spring, clean the plate and clean the EOS. EOS switches rarely need replacing, unless then are broken.
Don't f around with flippers. They are the single greatest thing that makes a game "feel" good. Even if you are hitting ramps, you will notice a difference, and likely the bats are misaligned.