Right now it seems you're only certain of one thing... You're losing coolant. Get your coolant tested and BE SURE that you have a BHG. There's no sense in selling a car on the suspicion that it has a problem when it can be confirmed one way or the other so easily. If you DO end up having a BHG, now is the time to fix it, not sell it to someone and lose money! Think of it this way... It's the PERFECT excuse to get ARP headstuds and an MLS head gasket so you can raise the boost and do other mods!
EDIT: Zerocool has a great point here... How much experience do you have?
EDIT: Zerocool has a great point here... How much experience do you have?