I've been using Biosyn in my Subaru H6 engine for awhile now, with good results. I started using it because of a fuel dilution issue. The fuel dilution still exists but I'm looking for a cheaper alternative to the Biosyn. I want to stay with a synthetic oil. A couple that come to mind are Pennzoil 10w30 and Mobil 1 10w30 HM. I haven't been a fan of Mobil 1 in recent years but the 10w30 High Mileage caught my attention becuse it's a little thicker and carries the ACEA A3 rating. I used Castrol 0w30 (German) in this engine prior to switching to Biosyn and it was OK but not great in terms of dealing with the fuel dilution. I still have some of it and will use it if there is nothing better out there. I'm interested in hearing from anyone who has an opinion on what I should be using. I want to stick with oil that I can buy off the shelf at my local auto parts store, so that eliminates Amsoil, Redline and the like.