Nugget Finder Advantage DIY repair?

I lent my 18" NFA to a "mate" recently. When he returned it I asked him how it went. "No good mate, false signals all the time."  

I gave it a test and it was falsing when bumped against rocks. Never did that before I lent it to my "mate"   

Because it is a few years old and out of warranty I thought I would look at it myself. There are no screws holding the mount on but there a three rivet looking things. After removing the skidplate I found three hard white plastic areas that line up with the rivet things. It looks like there may be nuts holding the mount on and then the nuts/holes have been covered/filled in with the white plastic stuff. Should I try to dig the white plastic stuff out or should I just send it back to NF for repair? I would like to get it fixed soonish because it is one of my favourite coils.

Mate don't play around with it, if you don't understand how don't create more problems and extra costs
when it goes wrong. They made it and they will fix if at all possible.
Cheers Dave