when my 2wd saff coolant was disapering i found that it was the h/g leaking water down the back of the engine block drivers side when the engine was cold it was visable but when it was worm it was bone dry. to have the h/g replaced it cost me £250 to have it fitted but i bought the parts, complete group a head set plus valve stem seals from pj motor sport which was quite exspesive in total it was just over £400.