on my 91 Vanagon with Manual Transmission I discovered a minor leak from the 13mm head bolt next to the tranny drain plug.  I threw a box wrench on it and gave it a few turns - it turned with light to moderate force.  After one full turn it wasn't really getting any tighter and the pressure wasn't changing.  Im worried it might be stripping out the treads on the inside so I stopped while I was ahead.    Is this common?  Any suggestions?  Its a nearly new tranny - about 40,000 miles since rebuilt by shop.  Although I guess regardless of rebuild those threads are still 20 years old......
BrettVancouver, Canada91 Vanagon, EJ22.