My '83 UrQ has 59k miles on it, and it's been run by the previous owner on Castrol Syntec (great oil, BTW) since it was invented, with no problems. I just changed over to Mobil 1 15w-50 synthetic, and have logged about 700 miles with no problems. If anything crops up, I'll keep the list posted. Regards, Tucker Fritch '83 UrQ