What would cause all of my valves to be very crusty from carbon and leak compression?

poor fuels and not being cleaned. try using a gas such as shell or mobile, one of the better gasses and adding in AMSoil Performance Improver (recomended every 4k miles) AMSoil PI will clean your entire fuel system. use a full synthetic oil instead of regular motor oil

I just had a 2001 Forester in the shop with 102,000 miles on it. I wanted to have the head gaskets replaced since this year was one of the trouble years for Head Gaskets. The shop found 3 valve guides dropped, one about half an inch. Subaru tries to tell you cheap gas and not changing oil causes this but that is BS. Guides are pressed in and carbon deposits form below the guide. Carbon is constantly wiped from the valve stem portion that enters the guide, so it can't build up and pull the guide out. The real problem is a poor design. Aluminum heads expand and contract at a different rate than the guides, which are a harder material. Over time, they work their way out. On Aluminum heads, they should be pinned in place, or some other means should retain the guide. The carbon deposits will preclude proper cooling of the valve and may contribute to additional heat on the guides but they should handle it, if properly designed. Subaru has a marginal design that can be affected by less than ideal circumstances but they try to blame it all on the owner. Total BS!

By the way, my Subaru did get oil changes every 4 to 5 thousand miles. No, I don't change oil every three thousand miles because that period was determined back in the old days when engines did not burn as clean and also suffered sledge deposits from the lead existing in the gas. Three thousand miles is way too often now days but the automotive industry is not going to tell you that. My wife did burn some cheap gas in it for a while but I xpect a Subaru to go more than 102,000 miles, even on cheap gas. I have has great experiences with Subaru up until the 2001 Forester. I have been very dissappointed with this car. The autmatic transmission needed replacing at 70,000 miles, the head gaskets are a known problem, and now I find out the guides were coming out. Sound like a GM car!!

There are oils out there that will aid in the build up of carbon in the valve train. Quaker state is an oil brand that is paraffin wax based oil that has cause many valve trains to gum up. I saw a 1998 Honda accord that used it and was so gummed up that the camshaft snapped in half. The company will lead you to believe otherwise but i have seen problems with it first hand