I own two vehicles that are between 65k and 85k. I've used Castrol GTX 10w-30 religiously since the second oil change in both vehicles. My last oil change I used Napa oil(Valvoline) and they both have started to seep a little oil around the pan gasket area? (3000 miles) Do the high mileage oils really have merit in reducing oil leakage? I'm curious if anyone else has had this problem when switching from one brand to another? especially, if you've used one brand for a long time.