could anyone tell me where the oil leak should be from?

more than likely it's the rear main seal on the engine. The seal itself isn't that expensive, but paying someone to get to it is. You have to pull the trans, clutch, flywheel off to get to the sucker. if its not that, then it might be the trans front shaft seal. either way the trans has to come out to tell. if the leak isn't bad, like a drop or 2 on the ground a day, you can probably let it go for a little while while you plan on what to do.

Try Auto-rx. Some people have had wonderful results.

None of the "stop leak" type products should be considered a permanent fix. if the engine is leaking, it means a seal or gasket needs to be replaced. Using coolant or oil stop leak products is just a good way to gum up an otherwise well-running engine. Fix it right.

Auto-rx is NOT a stop leak product.