Oil Leak

I have just bought a Seconed Hand Vax Cavalier. I didnt notice the oil leak it had. On further Inspection I put it up on Ramps and found there was a Bolt missing from the OilSump, it seems to have been broken off as I put a small screwdriver in the hole only to find the hole blocked, probably with the threads of the bolt . Is there any way I can get it to stop leaking oil without getting the threads drilled out.Regards Richard.