o-ringing t-stat housing

Green Cuda
I am having the same problem on my new 340 in my 69. the chrome t-stat housing just wants to leek.I had it off 3 times and even sanded it like you to no avail.
I found that the ends where the bolts go thru would bend downward,and on the manifoid, the metal around the bolt holes would pull up.I flat filed the maniflod, using magic marker to check it, and I did the same on the housing.I would put both pieces together and rub them, and where the marker comes off that is the high spots.When I first started doing it the housing would really wobble on the manifold. I'ts kind of a slow deal but it has worked for me so far. You can still use sand paper in the process to. the housing would rock back and forth like it was warped.when I stated.
After I got it Flat I put a beed of blu RTV all around the manifold and around the housing with the gasket between and bolted it together, and torqued it down, And it hasn't leeked yet. Might give that a try. Dave