I am not sure what they would charge. I have changed two on mine one when I just had the blower kit from a lean out detonation and one when I installed the ported head and pistons. I am getting ready to do another one when I install my custom head bolts (non Stretch type) Your could be the old style head gasket where your not losing cylinder compression just the oils seal area. Triumph made changes in the head gasket and for a while helped out on the replacements of ones that leaked. The question is how long have you had the bike and did it come with any type warrantee since it came from a authorized Thriumph Dealer who supposely blessed its reliability. I think they should have noticed something at the 20 K service. Parts wise you not talking much . Head gasket, cam cover gasket, tensioner gasket, water pump gasket, clutch cover gasket, (although I can change one without pulling the front cover) and Head bolts. I would first contact the dealer and see what they can or are willing to do for you.