We did un-spring the 2 heads with the worst buildup and found the guides to have zero detectable play in the movement range and very little as the valve was extended. The stems measured at .352 with no taper at all. We re-assembled and filled the chambers with lacquer thinner with zero leakage.
Here are some pics of my daughter doing the work as I watched/guided. I have 5 daughters and she is the one that got the motor head gene! A great garage buddy too.
I've had that spring compressor for 40 years and it's still coming in handy after sitting in it's drawer for the last 30 or so. A little mod to make it it in there nicely and she popped the retainers out.
I think this will eliminate the heads as the root of the problems.