y piece on 300tdi disco

hi been having probs with my discovery 300tdi using water,most prob headgasket which i will do when weather picks up.ive put k seal in it for now and its started leaking from expansion tank now,its done this before due to the pipe from thermostat housing and bottom of expansion tank being blocked.maybe the k seals blocked it again.has anyone ever fitted a y piece and larger bore pipes to replace the valve thing and the small bore pipes,