I now I'm probably jumping the gun here a bit, but I recently switched to Amsoil after running Castrol GTX 5w-30 for over 100k miles. People at work & my friends would think I'm nuts, so I gotta post it here. My dipstick has had a varnish on it for quite a while. I think I first noticed it around 30k miles. Today after only 500 miles with Amsoil I checked the oil & noticed the varnish was begining to disapear. The edges are a brite silver color now. Like I said, I know I'm probably excited for nothing, but I when I found this good news I had to tell somebody.