Jaguar XK engine OIL LEAK

A few oil changes ago I poured the contents of a small bottle (about 50 to 100 ml) of a Stop Leak additive to the oil and this caused the old asbestos and rope oil seals to swell and for about 18 months it worked fine although it was reccomended that it be added at every oil change. Just recently the old leak(s) have returned but I cannot find the product for sale anywhere. I have forgotten the name but I was sure I bought from Frost but it is not on their site. Can anyone help. Many thanks.