They all have minor differences, in all reality all of the modern Permatex Ultras will work just fine on the oil pan. Grey, Blue, Black, Copper, and the Right Stuff. Black supposedly is better for use on oil pans (mainly GM spec), but the Grey is also OEM spec on many different makes and models and is also used for their oil pans (Ford, Mazda, a few others.) The differences are mainly in meeting certain specs with the OEM's, I've used all of the new RTV's and they all work quite well. The Right Stuff is more money but it works great and cures extremely fast. The other ones will need more time to setup. That IMHO is one of the biggest differences in this application since all of them will be able to more than meet the heat resistance requirements.
