I have 1990 Jeep Cherokee with the inline 6. I ran dino oil (different flavors) for years, and it has suffered from coking, and a little sludge. I decided to start running systhetic oil, after I used engine cleaner. Now my only problem is that the rear main seal is seeping. I've read that Auto-Rx can recondition seals, but woud it be worth the time and expense of using it on a 13 year old vehicle? I mean, are the seals toast or do they still have life?