I have the same water leak behind the lower rear timing cover. It's been leaking for almost 2 years now, finally it's gotten to the point I have to put 1/2 gallon in every day (fill resevoir and top rad off). I am not taking any chances with head gasket sealing there so I am pulling the entire engine for a re-seal since it's been 9 years (on 4/20!) and she's got a multitude of oil seeps

I wish my engine had made it 10 years before doing this but oh well. Most other people's builds from around that time have already blown up so I can't complain too much XD