Michael, I just changed the fluid on my car. When I removed the pan I cleaned both surfaces COMPLETELY. I even used soap and water to remove all traces of grease, oil, or solvent. I then used a metric tap to chase all the threads on the trans case. Some of them were bad. I then used a thin layer of Form-a-gasket, the soft setting stuff, on the pan, placed the gasket on the pan and put another thin layer on the gasket. Before installing the pan, you need to check the pan for flatness. Previous owner or tech may have over torqued the bolts and deformed the pan holes which will prevent your new gasket from sealing. Use a flat edge and hold it on the pan edges and look at how it sits. Ball peen any holes down til they are nice and flat. Set the entire pan on a flat surface and make sure its not warped. I do not yet have a metric torque wrench so I just used the ol' "feel" method. I went around every bolt several times and snugged them up a little each time til everything felt tight and the gasket felt seated. I also used my wire wheel to clean every bolt completely! I used a dab of the same Form a gasket on every bolt. This is just my technique. I know a lot of guys who use silicone sealant and some guys who use nothing on certain assemblies. It worked perfect for me.

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Orland Park, IL
1985 300SD 215,000 miles