I thought it was just thermostat housing gasket, when i take out the thermostat, i saw it drip down on this area. it not the thermostat housing gasket, it kinda back their a little.
well it stop leak I think, I put the new thermostat housing gasket on, and fill it with water and it leak, I take out and put some black rtv ( black rtv is only 1 i have atm, ITS OK ? ) put some black rtv both side of gasket and now no more leak.
The black will be fine. Ive used the orange RVT and a gasket and not had any issues. You have to be sure the surface on the intake side and the thermostat housing are both clean, scrape them both with a razor blade and clean them off with brake/parts cleaner. I put a few dabs of RVT on the thermostat side and gasket so that it does not move then put a bead around the other side of the gasket that touch's the intake and let it set up for 10-15 mins then install it. The other thing you have to watch out for is the thermostat its self slipping down b/c if it moves off the ridge's on the housing it will not seal right. Ive also put a few dabs of RVT on the thermostat its self and on the side where it touch's the gasket to keep it in place so it will not move.
Most likely it's dripping back into that location from the thermostat gasket. It is very common for the thermostat to drop out of the groove during installation. If you tighten it down after this happens, it warps the crap out of the housing, and it won't seal no matter how much goop you shove in there. Check the mating surface of the thermostat housing with a straight edge. If it's warped, don't sweat it too hard, it's like a $12 part at any autoparts store.