Brake reservoir screw head issue

[satchit]

Not sure what your mechanic was thinking about, but if you drill the head out you will not touch the threads. it will just take the top of the screw off and leave the shank in place which you remove after you take the reservoir top off.

The mechanic was concerned about drilling too deep.

My concern is drilling too wide - I've gouged out a fair bit of the head. So, I'm going to need a small dead center pilot hole.

I've ordered one of [url=https://www.thegrabitstore.com/collections/featured-products/products/alden-4507p-grabit-micro-broken-bolt-extractor-4-piece-kit]these - which should handle the M4 screw. Will be delivered early next week. I'll probably start with the smallest one and if that doesn't work move on to the one for the M4 screw.

If the above doesn't work, then I'll move on to the destructive approaches. pekingduck's suggestion for just cutting the cover is a good idea.