I have seen loc-tite and or interference screws used in the type of application you describe. Manufacturers are more concerned with vibration loosening the parts than you being able to easily service. They want to sell you a new expensive part.
You may have to drill those heads off.
You may find a better quality allen bit socket somewhere too.
That thought occured to me right after I snapped the first Allen bit. I stopped into AutoZone to get a replacement, but they only came as part of a full set. I settled for a new set of standard Allen wrenches (which I needed anyway).
I will still look for a high grade replacement bit, as this probably won't be the last time I have to work on my machine.