So, the new short chainring bolts I ordered arrived, complete with Haribo, in the usual speedy manner which I expect from Wiggle, and I went to fit them.
However, I discovered that the idiot who had assembled the bike originally had blindly assumed that short bolts were required without doing his due diligence 😳 The Gates Carbon Drive belt pulley (as opposed to a chainring) does not have counter-bored bolt holes, so normal length bolts are actually required. The short ones had the sleeve only protruding through the pulley, not into the crank-arm, and the threads were loose in the arm. This means the pulley was free to move a bit, making it understandable how the bolts came loose, chewing up the crank-arm holes in the process.
Normal length bolts duly ordered and I’ll have another attempt to rectify when they arrive!
Cheers, Rich