Actually. I did it again with different results. Maybe not enough grease the first time.
What are the chances that the top of the valve is either out of round or warped? Or is it more likely that the head is warped?
I ask because I just put my drill in a vice and the valve in the chuck. It looks to me that the top of the valve kind of wobbles a tiny bit up and down. The stem looks straight. It's tough to tell though by the naked eye though. I thought of rigging up a crude dial indicator but I can't say for certain that if I found any movement in the stem it wasn't due to my chuck being slightly out of wack.
Edit: Maybe the most logical thing would be to get a new valve. I know that's not the most scientific method but I think it's like $20. Not that I'm quitting on the diag process. Just spitballing.