Well your not alone on this one...Module 4's that have been in service for some time see this all the time between the dissimilar metal, heat, and straight-up muck.
Right after Boxing day, we are running a few of these through our repair facility at the moment...
After stud and Helicoil removed we will work on the next step CLEANING and RE-INSTALL of new Helicoils...
Let us know if you need any assistance with the process or just send it our way.