Some dip is normal on games with AC flippers. All you can really do is gap the EOS closer. That drop does look a bit more than I'd expect but not a ton

Buzzing is inevitable too.

Not a bad idea to fit new EOS switches and flipper cabinet switches too. That way, max voltage is present right through the chain.

Without a schematic, I don't know what the voltages should though I thought WMS machines of that era used 24v AC [ used to be 50v on earlier games] You might want to look at Pinrepair as I'm sure there is, or was anyway, a list of coils values, measured by resistance rather than voltages.

My point was though that from experience, Its a good idea to replace all the electrical switches that feed up to the coils. And, you might want to check your coil stops and flipper plunger to make sure they are good. Again, I prefer to change the lot if they look worn.

Change the coil stop. When the coil stop becomes magnetic the hold gets weak and you get the recoil you describe. A good part of the hold is due the plunger magnetically attaching to the coil stop. Once the coil stop itself becomes magnetic this doesn't seem to work all that well anymore and it weakens the hold.

Actually, the kick that the flipper is imparting to the ball is typically a result of the EOS gap being too small when the flipper is all the way up.

What is happening is that the momentum of the ball is causing the flipper to bend downwards slightly (completely normal) to a point where the EOS switch contacts re-enagage and the low-power side of the coil is short-circuited, which then causes the high-power side of the coil to force the flipper back upwards. This effect pogos the ball off the flipper bat. What you want to do if the pogo effect is excessive is to re-gap the EOS switch so that it opens sooner, and thus has a larger gap when the flipper is at the end of its upward travel. However, you don't want to open the gap too far or you will lose power on the flipper up stroke: it's a trade-off.

I think replace that Stop, and I agree with trying the larger eos gap, post results!

PBR sell rebuild kits which include the stop, spring, plunger, sleeve, etc. Well worth doing

To me, the pbr mini kit is overkill and was designed to make $ on the uninformed. You can buy the stops, springs, plunger/links, sleeves and bushings for $22. The kit will cost you $36..you'll get some extra stuff like eos switches and screws, but those are usually unnecessary.I never buy the springs either since they are usually ok or an be given a bit more resistance by stretching them a bit.