[tubman]

I'll take the contrarian view again. In 1987, when I bought my '67 corvette L79, it had stripped threads in the intake where the thermostat housing mounts. Being short on equipment and experience back then, I used the "Loc-Tite" thread repair product mentioned above. It obviously worked, and I forgot about it. and used the car almost daily in the summer for 30 years. A couple of years ago, I had the opportunity to replace the valve seals, which required disassembling the top of the engine. While removing the thermostat housing, I suddenly remembered those long ago repairs. On assembly, I took a good look at the threads in the manifold and re-assembled it as is. (I did replace the thermostat and gasket, though). It didn't leak this time either.

It obviously worked satisfactorily, and after my experience, would suggest it for repair of the type of problem you have. It has the advantage of not affecting the original part, unlike the other methods. You can always step up to one of them if it doesn't work. My experience discourages me from any kind of welding on old aluminum castings, and there is the problem of thin margins with any type of threaded inserts.

There is really no ideal solution for all situations, but I think it would be a mistake to reject the "Loc-Tite" solution out of hand, especially if there are some threads left.