Rounded out

[SupermotoDave]

Just pulling the heads on my X2 and the cap head down the pushrods tube has rounded out despite me using an unbrako Allen key. Any suggestions? I have 3 ideas at the moment but interested to see what comes up.
Considering all the other things I have found over the years I am still tempted to ascribe the PO to this one, and not looking forward to what I will find if I have to go deeper.
Cheers
David

[EVguru]

Try the next size up torx bit. You'll have to hammer it in, but it often works.

The next step is to drill the head off. If you use a left hand drill bit, then there's a fair chance the drill will grab in the fastener and just unscrew it.