Best thread sealant for exhaust studs into water jacket

I did a search and found a post from someone who recommended Loctite 567. However this is absolutely not the ideal sealant. I am talking about the end exh manifold studs that go into the water jackets. Loctite 567 is not a thread locker and is classed as a low temp (max 150 degrees C) and low strength pipe and thread sealant, not recommended for vibrating parts. These studs are within 10mm of the exhaust port (600+ degrees?) and in a fairly harsh vibrating environment. More ideal would be Loctite 5770 which is a medium strength, high temperature (275 degrees C) thread locker and sealant and suitable for areas in constant vibration. Also there is Permatex high temp thread seal which is rated to 400F or 204 deg C. There is also the good old Aviation gasket sealant, been around since the '40s, however that is only rated to around 175 deg and goes very runny with even normal engine heat. My problem is that due to the mild corrosion in those threads and multiple fasteners being screwed in and out, the studs are not screwing in nice and firm, there is quite a bit of movement of the stud so a good high temp sealant is needed. I will have to keep looking as I believe that the threads in this area on a hot day (and we get some damn hot days 45degrees+) would well exceed 400F. Combined with the high pressure of the coolant there as well.

BTW, one hole has been tapped out to 3/8" but is still not tight anymore, the others are 5/16" but I am not pulling the heads off to retap them. Thanks for reading.