I was about to say a collapsed ring in #3, then I read that you had it back up...
Unsure how you can "unstick" a sticky valve when jiggling the ignitor...but hey.
As for the low compression test, yes a stuck open valve WILL give a lower compression reading, a leak down test shoudl then be done to find out why.
As for why it now has compression of 120psi, I have NFI, sometimes they stick but I would be running a flush through it, RB20's have hydraulic lifters and as such it might be the cause the the stuck valve...I am only assuming cause I cannot hear it nor look at it...