[KTL]

Drill out the snapped screw altogether with incrementally larger bits until you can reopen the threaded hole. If unsuccessful at reaching clean threads, then drill and rethread to the next size bigger if possible.

Don't bother with JB Weld. I think that stuff blows.

Are you updating the cross shaft or has the update already been done? If the update hasn't been done, then the old shaft is most likely garbage. Can you weld a new, bigger screw to the shaft itself? Replacement updated OEM Porsche shaft isn't all that expensive @ just under $40.