So, I decided to remove the scope mount hole plugs from my Marlin in anticipation of either a scope mount or an aperture sight. I broke out my gunsmithing screwdriver sets and got to work. The very first plug I tried to remove was jammed as tight as any screw I've yet come across. I managed to bend two bits and break another and I still didn't get the blasted thing out. Trying the other three yielded two that were simple to remove and the last is just as stuck as the first.
Despite what one of my coworkers has convinced himself of, I do not believe that thread locker was used on these two plugs. Firstly, only two of the four plugs had issues. I can't believe that only those two would get locking compound. Secondly, none of my Marlins have ever had thread locker on the plugs. I doubt they've started now all of a sudden.
At any rate, now I have two buggered-up screw heads and no way that I can think of to remove them myself short of purchasing a screw remover setup. I have no desire to risk sending this back to Marlin with them packing up the factory and all, so I guess I'll be sending this one off to the local smith.