On the newly acquired R60/5 (1973) when I checked the drive shaft fluid, I removed the top bolt (not an allen hole) and saw a piece of metal attached to the threads on the plug/bolt. When I tried to tighten, it started spinning.
If it were the bottom I'd be more concerned - wondering if I could either find a longer bolt or use a little red or blue loctite to hold it in place between maintenance cycles.
Otherwise, I could remove FD, take it to a machine shop and get it re-tapped for next size up or heli coiled.
Open to suggestions.