Welcome Tenente. My advice would be to leave things as they are and save yourself the expense. What has happened is unfortunate, most of us don’t apply anything to liners as they can be very delicate. To replace a liner, both visors have to be taken off. The remnants of the original liner are removed and every stitch hole has to be cleaned out. Next a new liner has to be cut out of vegetable tanned sheep skin and dyed on both sides. Finally, that liner has to be hand stitched back in as well as both visors. Obviously, a great deal of work is involved which translates to hundreds of dollars in cost. I would not spend the money on this M15, just learn from your mistake.