Its most probable your headgasket has gone again or the liners have moved, in which case its all got to come off again. You wouldnt be better off buying a second hand engine, sorry but thers no need repairs should cost 550-600 tops. If you have the new multi layer style gasket fitted you should find that much better as we have fitted loads of these to vehicles and have yet to have any come back.
Oh and btw i work for a Mg/Rover specialist
Jd
January 2009