Allen head and Cheesehead bolts can be extremely difficult to remove, particularly on 944 engines. Since most of the 944 engine is aluminum the steel bolt thread tend to bond to the aluminum. Because of this, almost everyone who has ever worked on a 944 engine has stripped an Allen head or cheesehead bolt at some time. To help prevent this, I'll share this tip I learned from a mechanic friend of mine.
"Waking Up" the Bolts
Using a punch or socket extension and a hammer, tap around the outside head of the bolt.
For Allen head bolts, tapping on the inside of the Allen head opening with a punch and hammer is effective as well.
While attempting to remove the bolt, ensure that the Allen head tool or cheesehead socket remains inserted straight into the head of the bolt. This requires using two hands, one to hold the tool straight into the head and the other to turn the tool.
If the bolt does not break free easily, tap the head again.