Depends where the leak is from. If it is a rotating seal like a rear main or similar, I would try AutoRX.
If it is something like a valve cover, you migh temporarilly seal it with a crude seal swell additive from your local autoparts store.
If the leak is less than 1qt/1000 miles or so, I wouldn't mess with it at all (I espicially wouldn't use any seal swell stop-leaks).
The upside to AutoRX is that it has an overall benificial effect, and they are nice to deal with if it doesn't fix your problems.