I'm thinking about trying Restore after seeing this Project Farm video(Part 2, one year later)
Restore compression test 1 year later
Any other suggestions? Since the GP hole is so easy to get to I'll test it again a few times and see how she does.
It’s unlikely that you have one cylinder that’s got varnished rings, but it’s not impossible. I recommend AutoRX as one of the only fix in a bottle I’ve ever used with excellent results every time. It’s hard to find, but worth it for applications where you need a slow but effective cleaning agent (IDI that hasn’t been worked hard as an example).
I know you don’t want to pull a head but if you figure out it’s truly valve related it’s not the worst job in the world.
Good luck whichever way you go and thanks for posting the experimental results