Thread sealant

GM used that liquid Teflon sealant up through the early 90s. Then, they posted a massive TSB saying not to use it anymore and for all the dealers to discard their remaining supply.

The replacement "stuff" they started sending was GM's version of high temp RTV.

I asked a GM rep about that afterwards and he said that both liquid Teflon and the Teflon tape was more geared for pipe threads and also they were having problems with the liquid Teflon not holding up to the heat.