Was this done on a 'mates rates' basis Dave or normal rates charged ?? If the latter I would have the mechanic back to rectify the problem he has either induced or failed to cure
If not, and I appreciate your situation. and just to be clear, this leak is from one of the joint faces which he split and would previously had a fibre gasket ?? did he clean all traces of the old gasket off before blue ginking it ??
If so, my suggestion for a cheap way may be to drain the oil out, slacken all the joining bolts a little (after solvent cleaning the joint around the leaky bit) if by selective wriggling or jacking you can get enough of a gap to introduce some new jointing compound (I've generally used Hermatite) with a feeler gauge to spread, then pull the bolts back up - dirty but might save the hassle - and others might like to comment on the advisability & safety before you try.
Otherwise, degrease around the leak (after draining) and smother in silicone rubber sealer, refill when cured and pray to the ancient blue gods
Best of luck with it Dave