Talked about this here maybe a year ago. I had the same problem. Technically you are supposed to replace the thermal protector with an OEM part. But the fixture I had was 30 years old., so that wasn't going to happen.
The thermal protector consists of a bias resistor across the line and a bi-metallic switch that is influenced by the heat given off by the resistor as well as the ambient temp. When the combined temperature exceeds the rating because the sensor is packed in insulation, the bi-metallic switch opens and turns off the lamp. So the lamp wattage only matters when it causes heat to build up under the insulation the fixture is covered with.
I did find a supplier (I think I Googled the original manufacturer and part number off the switch) and came up with what I figured to be a suitable replacement from the available temperature ratings. (163 deg sounds familiar.)
Now, with all that said, the fixture was being used with a CFL which I changed to an LED. How much heat do you think that's going to produce? Sure, someone could put a 100W incandescent back in there. But that's not likely today. Somebody from here suggested to put a big sticker inside that says "LED ONLY". Sounds like a good idea.
So, unless you or the customer are willing to replace the fixture with a new one and accept the collateral damage to the ceiling, I would just do as I did or just jump out the sensor completely and require LED lamps.
-Hal
