How do I fix a leaking trap. It's upstairs and hard to get at. Is there a drawing of a shower trap which might help

Most likely have to go through the ceiling below. How do you know the trap is leaking? Could be seal between pan and flange.

Do you have a custom tile shower or a manufactured base and enclosure? Does the floor flex a bit when you step on it? If the answer's yes you may be able to caulk the drain and stop your leak. If a custom tile shower open up the ceiling and look for moisture at the highest point. That's where you'll find the problem. Good luck, Tom

I would use Harold's approach: cut the ceiling, replace trap, and patch the ceiling. It is the best - and maybe also the only - option you have.