Stop in for a cup of coffee

On another web site. People listen to this crap
You can usually tell if you have a rear main seal leak by connecting a mechanical oil pressure gauge when the engine is cold and test the pressure, it should be around 60-80 PSI, of course give tolerence for age. Then let the truck warm up you can drive it to do so, then go back and connect the mechanical gauge, the pressure should be around 40 at idle if it's lower most likely you have a leak. don't use the oil pressure gauge that is built into the truck because they're not always accurate, you're better off using an old fashion mechanical gauge.