There's a few different things you can try. Inspect the housing and intake for cracks and make sure the housing gasket surface isn't warped. You can hold it flat against a piece of glass or other flat surface to check it. Look closely at the gasket surfaces for damage or pitting. If everything looks good, you can tackle it several ways. You can reinstall it using 2 gaskets. You can put a thin layer of rtv on both surfaces, let it dry, then install single gasket as normal. You can run a small bead of rtv and reinstall the t-stat and housing loosely. Wait 24 hrs, then tighten the bolts. If, after any of these methods, you still have a leak.... then there's either a hairline crack (probably around the bolt thread area on the intake) or a hose is leaking near the housing and it's being mistaken for a gasket leak. This would most likely be from the small bypass hose on the water pump.
I know leaks in this area can be frustrating! I've been through it a few times. Also, keep in mind that new t-stat housings are available, but they're notorious for being of poor quality. You can sometimes true them up with some heavy grit sandpaper on a hard flat surface but it's best to just get one from the parts store and inspect it well before you leave.
