I wanted to add to this....
My KING KOOL has a weak kicker as well, and working on it has varied performance. Finally I was able to get a BLADE from a flipper switch and do the repair described so often on Pinside.
Results: minimal.
What I DID notice it helped with was ELEVATING the ball tray bringing the ball to the plunger. That is probably what it is doing for most people. Someone had already put a washer under there, and the ball would sometimes be stuck on the switch in the ball tray. With the switch's blade it elevated it enough so the ball wasn't stuck on the wire switch anymore and it would either return to the kicker or go to the plunger. THUMBS UP for that.
However, I did get into serious observation of the kicker and found it was INCONSISTENT. Sometimes it was strong, sometimes weak. The power was variable. So it is most likely the switches being gunned up.
Compound problems did appear as I took notice, though: the coil shifts on its bracket and doesn't sit flush. The coil leads had arced to the kicker arm in the past, maybe recently. The mechanism was slightly gunked up with old grease. The coil plunger is slightly eroded/tarnished and might catch on the coil sleeve...
Ultimately, there are half a dozen problems there. It's probably the 50-yo coil as well, but most likely in good-enough shape. Someone was in there before and did some funny business to help the mechanism, but nothing worked perfectly.
