Your not going to like this answer.....but if there is damage to the mount itself then there is really not a lot you can do for the damage that has already been sustained. However, you can prevent further damage.
Moths, mites, and beetles such as 'carpet beetles' that are common for this area can get into mounts and start to chew on the hides and in particular the roots of the hair follicles, causing hair to come loose and fall out. Look for areas around the antlers/horn pedicles and back of the mount where the hide is glued or stapled to the backing board base; this seems to be the starting area for most critters that like to chew on the hides. Don't look for actual bugs as most of them are pretty darn good at remaining hidden and very small, especially mites. Look for damage or hair coming out or falling off. The hide/leather can also appear to have very small chew spots on it which mimics a porous look to the leather.
The best thing to do is bug-bomb your trophy room or mounts at least every 6 months as preventative. I use the Hot Shot brand bug bomb. I've used different brands, but this one seems to penetrate areas very well instead of just surface protection, plus it has a deodorizer so it doesn't leave a harsh chemical smell. My dermestid (flesh-eaters) beetle colonies are in a completely separate building from my main taxidermy studio, and I have a stringent process of ensuring no bugs come through on euros to the studio for whitening of the skulls, however I still bug-bomb about once a month as a preventive.
What I would do O.Hemionus is get a big black plastic bag, like a 55 gallon commercial size. Put the mount in the back and set off one of those bug bombs in it for a concentrated effect. Let that mount stay in there for half a day and then remove and let it air out for an hour or two be putting back to its original spot. I would also bug bomb the room you have your mount in as well. Hope this helped.
Joel/BRT
