You had a stuck valve, thinking you also might have stuck rings.
Could try a snake oil treatment of ring free of sorts,or some penetrating oil
sitting in the bore for a while.
Might work, might not, but @ this point you are just playing, so no harm no foul
Also could try some in the crankcase and just let it sit and idle over a period of time, many times over,creating heat/cooling cycles.
But honestly, it is prolly plum tuckered and needs "refreshed"
