I have a 2004 a41.8T and I recently changed my oil for the first time using Amsoil 5W40. I just checked it today-about 1,000miles afetr change and notices bubbles on the dipstick. Is this normal for the oil to have small bubbles. The oil also looked a bit thick and dark considering it only has 1,000miles on it. Should I be concerend? i know sludging is a big issue with these.