I keep hearing this, yet no one has opened up their P-mag to check the heat range spec's on the components within the units.
I don't know of one documented heat related failure.
So what is the deal with the temperature tell-tale stickers? 200F, yes?
BTW, the temp sensor on the EI box never exceeds 106F degrees behind the engine plenum flying.
Which merely indicates that your installation has rather poor heat transfer from engine to air, or a lot of cooling air leakage. It's entirely possible to exceed 200F air temperature in the lower/rear cowl volume.
Operating with the cowl exit wide open (maximum mass flow) last June, I was measuring 165F air temperature in the upper firewall area at cruise speed, and 185F in slow flight. I have recorded exit temperatures as high as 228F with high power, low speed, and exit closed for minimum mass flow.