OK, another question, this time on the VW 2.8L used in the B5 Passats. My dad's noticed that the B5 consumes a fair amount of oil, up to a quart per 1,000 miles, in mixed driving. He's always followed the 5k OCIs per the book, using conventional 5w30. He's noticed that Castrol GTX (which the local shop uses) seems not to boil off during the first 3k (compared with other oils that burned off almost from the start). The boil off is raising some concerns about sludge or varnish. He's thinking of trying Auto RX (or a similar product) before the next oil change. I suggested perhaps just having the local shop add a quart of GC or M1 to the next oil change, or perhaps just switching entirely to synthetic. The 2.8Ls didn't get the "sludge letters" but apparently on VW's site they recommend VW 502.00 for all their engines now, even the non-sludgers. He seems a little reluctant to switch to synthetic after using conventional for over 60K. Any opinions as to either idea? There's not much on the GC forum on this topic from what I can tell by searching.