I would leave it at this point. Welding another bolt on is always a great idea. When I didnt have a welder, try to thread two nuts onto the stud , one at a time if you have enough of it still showing. Then tighten them together. Then put your wrench on the inside one and loosen. You may get lucky . If not, get drillin'!

I have broken a bunch of water pump studs on my 944s. A real hassle. But a necessary evil.

Good luck !

__________________
Patrick Leber
'84 190E 2.3
'83 Porsche 944 (track car)
'84 Porsche 944 (parts car)
85.5 Porsche 944 (sled)