You used tape or paste? I'd give it a shot by draining the coolant and then taking the stud out and cleaning the threads, reusing sealant and reinstall. Got nothing to lose for sure... And I did mention using sealant, not tape!

lol... I'm just repeating all I've read, tape is NG. I'm just not sure how good an idea is to un-torque one bolt from the head without doing all? Others can chime in on it though. ; )

good luck!