Well the same garage had another look for me, after you guys and Rob Sport said it is possible to drill the sheared bolt out. They agree now, but we still have the lower rear bolt to remove and I tried that as hard as I wanted too. Garage chap will let me know about him drilling out.
Anyway, as a bit of research one area on the manifold/cyl head that I know leaks, I rubbed in some std. exhaust past and left over night. In the morning I could not believe how much quieter and smoother to drive. I know this is only a temp fix but at least I know whether most of the leak is.I have also now discoverd the product I could use as a less temp repair, as per my earlier posting, its called Thermosteel, a one part type epoxy solution, resists up to 1300 deg C, so might try.