Im looking to do an oil change. Im starting to get the normal weeping at the rear main seal. Its not leaking but I do see some blow by under the car. Its a 4.0l with 220,000 and its an AMC in-line 6. 1) So with that being said, what is a good high mileage engine oil that will help to sell seals? 2) I would use 10w-30 normally, but with it being a higher mileage car should I run a higher weight oil? 3) What about rotella 15-40? I know its not high mileage, but I know its pretty good. 4) I think Id like to go non-syn just because the "synthetic" can leak thing plays over and over in my head haha. Is that true that 100% synthetic oil can leak in a high mileage car? 5) Also, I was wondering about running TCW3 oil in my gas will help the idle and starts better? If so how much? 4) Also, should I maybe run a good oil with detergent in it to help clean the engine out? I picked this up, so Im unsure on the history. Or I could run something in there now ( like mystery oil or something ) and then drain and fill with high mileage oil. Thanks!!