On the RV-8 I'm helping to build, also an IO-360, we bought some AN900-10 (same thing as MS35769-11 according to Spruce) crush gaskets and while they fit exactly correct around the 5/8" threads of the oil temp sensor, the fit looks dangerously loose around the machined-smooth shoulder/shank that lies in between the hex head of the sensor and where the threads begin. It looks like if the crush gasket isn't held exactly centered when the sensor is tightened down to squeeze the gasket, that it might be prone to leak there due to the large gap between the inner diameter of the crush gasket and the smooth shank of the sensor.
Has anyone else noticed that on their oil temp sensor? This one looks like the smooth shoulder was perhaps lathed down too deeply or something.
Would it be a bad idea to put a rubber O-ring in there to take up the gap?