Response Trigger!!!!!!!!!!!!

First, and I don't mean to be insulting with this question, did you remove the powertube/valve assembly completely from the right receiver half?  If you did, try the following

• Make sure you hold the powertube by the body, not the thin neck (I've seen them broken that way)
• Experiment with different wrench sizes (since it's starting to strip, a smaller/metric size might fit tighter to prevent further damage)
• Be very careful if you have to use an adjustable wrench, they have a tendency to loosen slightly and strip the edges off nuts
• If you've never had this piece out before, it will still have the original thread sealant on it which is, in my experience, a bear to break loose-it will require a little bit of force

Good luck