Slightly different but I stripped the thread on one of mine from over tightening it. Didn't notice at the time & it didn't start to leak oil until a month afterwards.

I measured the length of the bolt, measured the depth of the hole, discovered that there was a good 10mm of hole left with no thread so tapped a thread all the way to the end & used a longer bolt.

Doesn't solve the problem of getting a snapped bolt out though sorry.
If "your mate"

removes all other bolts can he get the cover off & expose any of what's left of the snapped bolt ? Enough to get a multi wrench type spanner on it or weld a bar to it perhaps ?
I hoisted the front of my TRX up as high as I could with the rear on a paddock stand in order to gain good access to the whole under side. It all helps when you're struggling your nuts off to do something like that.
Good luck with it.
