The other 3 screws came out fine, guess there was a tad too much locktite on the 4th.  How can I get this screw out?  Any advice is appreciated.

One way to break the Loctite is to heat the head of the screw up with the tip of a soldering iron.  The heat should loosen up the Loctite and allow you to remove the screw.  Hopefully!

^ that. If you can heat the head only and have the heat transfer, then if a allen will fit again, try it. If an allen doesn't fit try an easy out. You may be able to get an allen to fit from a metric set again, try a bunch if you have them.

If a soldering iron isn't hot enough, a heat gun should do the trick

I'm not familiar with that mount, but I had one of the screws stripped in the 3inch rail on the side of my obr. I tried a heat gun and soldering iron and none of it worked. I tried heating it up and putting a rubber band on the tip of the  Allen key, still nothing. I ended up buying an easy out stripped screw bit and it came out in 5 seconds. Easy to use and if you are careful and the screws are not recessed enough you should be good.