Brad, first I recommend to confirm if the leak is engine or transmission oil. Perhaps you have done this.
There are several products on the market to add to your oil in order to stop oil leaks. First you must accept that all old cars even some new ones do leak oil. I purchased my Pagoda in May 2013 and she had minor oil leaks in both the transmission and motor. I used several products in the oil to stop leaks. Finally now after driving nearly 6000 miles in 26 months and about 600 miles this summer my oil leaks stopped.
What I am trying to tell you is first establish where the leak is coming from, then try one of the "stop leak" products, you need to drive the car a fair bit on longer drives to se results, as I mentioned my car still leaked oil last year even after a 1600 round trip I made to Williamsburg. Finally this year after driving some 600 miles so far no more leaks.
So before you put your hard earned money on the table at some shop try one of the products that have worked for people in your area or ask your mechanic. You mentioned that your engine runs well, so did mine and that is why I tried the stop oil leak product first.
My neighbor did too on a 20 year old Cadilac, when he sold it and the new owner called him later after a 300 mile drive home he said "no more oil leaks"
So there is something to be said and tried first to re activate those old rubber seals ... Try it first ... Goog luck to you!
Here check this first link and others on Google after you type it into Google ---> stop oil leaks in engine