oil pan leak in rear by starter.

If the leak is around the oil pan, where the block meets the pan. You can do a temp fix by cleaning the area good with something like spray brake cleaner. Then run a small bead of RTV along that edge press in with your finger and let dry. If it is from the bell housing area, it may be a rear main oil seal. They do make a stop leak product that you add to your engine oil. But I have never seen it really work.

Please don't use any 'stop leak' products; never a good thing... The external RTV is always worth a shot, but usually only modestly successful. I can understand your intentions, no seal or gasket repair there is cheap or easy.