Mark I also had a small rear main leak in my 327 and a good friend recommended using Lucas Stop Leak. My motor was down 1/2 quart so I topped it up with some of the Lucas stop leak. I took the car for a short trip and parked it . Next day I backed the car out and guess what no leak! It appears to do what it says because I have seen no evidence of a leak in the last 3 months since using it. A good product that you add to the oil and it refreshes the rubber rear main seal (that is prone to drying out) as well as the valve seals. Worked for me and worth a try for under $20
I have actually thought of using some kind of product. Years' ago I had a 5.0 Crown Vic that developed a serious main leak. I added a product made by Eagle I think, and sure enough it stopped.
The problem is, this is a new build with all new seals. I was super careful, but I suspect I may have nicked the lip, or didn't seal the cap corners correctly. I did add some Ultra Black to the partings and the corners. The sealing surface on the crank was good.
When I ran the engine up on the stand, sure enough the sender fitting did leak. And it leaked down the back of the block. I fixed that up, and never assumed it could have also been a main leak. Just checked the sender port again. Bone dry.
I guess I could try some product. Is there any downside to it in a new motor?
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67 Grande Parisienne 4 door HT. 69 Parisienne Convertible.
