Matlis on klaf mashuach

A friend has asked me to do some basic repair work on his shul's megillah - it appears to be approximately 75-100 years old, and the lettering is virtually pristine, so in terms of reinking, it shouldn't be much work.  The larger problem is that the edges of the klaf are weak, and there are places where the klaf is almost torn/very heavily creased.  (In at least one place, the klaf has been reinforced with scotch tape, which I will obviously remove, and have told my friend that this is, to say the least, sub-optimal.)

My plan is to use thin matleisim around the border of the megillah to reinforce as necessary, but there is one problem - the back of the klaf is mashuach and very, very crumbly.  (The front, luckily, seems to not be.)  My feeling is that if I glued a matlis to the klaf, it wouldn't adhere, and, to the extent that it did, the matlis would come off with the coating quite quickly.

Does anyone have any suggestions for how to deal with this?  I was considering sanding off the coating and then gluing, but would appreciate advice from others who might have dealt with this issue.

Kol tuv, and thanks!