Hello everyone. My subaru is leaking oil from the head gasket and is getting worse since I started useing Rotella T5. I used it because i thought it would be pretty thick thus slowing the leak. I noticed it leaked alot slower with Castrol High Mileage but i hate castrol products. Im thinking the T5s higher syn content is why its leaking more. Would a conventional High Mileage oil like Pennzoil be better? Im trying to slow the leak and not put more than the cars value into getting the leak fixed. Thanks in advance to all who answer.