Master cylinder screws.

[Flak]

If you get some "Go Through" screwdrivers and tap the top of the screw driver with a nylon mallet it shocks the corrosion holding the screw in, it also seats the screwdriver tip into the recess more and 9 times out of 10 the screw will come undone.

It also helps to know the difference between a Pozi-drive screw and a Phillips screw and use the appropriate screwdriver so you don't mash up the recess in the first place.

They're probably neither of those but JIS.