Are you positive it's the head gasket?
I was losing water in mine when i first got it and this was the suspected cause of loss of water and over heating etc. Turned out to be the expansion cap.(serviceable item) wasn't allowing the pressure to build so the water was escaping, this along with a hair line crack in the expansion tank was the culprit!!
Wouldn't drive it if it not right, ye'll just make it worse.