I discovered the rear seal leaking on my 351C a few days ago. It had been leaking a bit since I bought the car a year ago, but really didn't know for sure where the leak was coming from. I'm guessing a labor intensive job to replace the seal since I'm not a mechanic (or if I was, allot of labor involved). Someone educate me on the stop leak stuff they have out there. The only thing I know is that you put off the inevitable, (sic) repair.