I watched One of John Mummerts U-Tube Videos regarding installing Oil Pan. He uses Permatex Grey as a Sealant on both sides of Pan Gasket. On the Block and Oil Pan. Is there a reason for using the Grey instead of Black? I also watched His Video on installing Rear Main Seal. He mentions that He believes the majority of Rear Seal Leaks are NOT the Seal itself but the Side Seals. He showed how He coats Side Seals with Silicone to hold in place on the retainer and then installs the retainer. My Question is why are the Side seals still being used when the Space where the Side Seals go could simply be filled with Permatex "Right Stuff". I can tell You from experience that doing it with "Right Stuff" will not Leak. I did mine a few Years ago and had no Leak. when I took it apart to rebuild it I had to cut the sealant with sharpened thin Putty knife to get the Retainer out. It would flex but not separate with the Bolts out. The Side Seal Space will not allow Oil to Leak if filled with Sealant. He mentioned in the Video that in the rare Occasion that Rear Main Seal does Leak when installed His way He simply redoes the Rear Main Seal. I like my way much better than even His way of doing it. Thoughts? 

  

I agree the rear min seal itself often takes the blame for side seal leaks.  There is constantly new advancements in sealer technology and "the right stuff"  may be the best substitute for solving the side seal issues. I have had experience with a fairly new caulk that has excellent adhesive characteristics and holds up when filling large gaps even when flexed and can be applied to somewhat wet surfaces. It is supplied in a clear tube for caulk applicators but I can't remember what it's called. So why not develop the product for the  automotive world as well? At this time, should I rebuild another y-block, I would try it.  Why not buy a tube and experiment?  

64F100 57FAIRLANE500

Well  I am in the process of re-building mine. Using "Best" Gasket Set which includes rear Main Seal. I will be using "The Right Stuff" again. I like the Odds much better using the Sealant rather than Side Seals. The Rear Main Seals was a problem right from the Time these Cars were new. Not a great design along with the Original Tin Valley Cover. I have a New Mummert  cast Cover to go on mine. Another potential leak fixed. 

  

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I use the Ultra Black RTV as it tends to be more pliable when it dries than the ‘Grey’ series.  The Black does require longer drying times and overnight works for this.  If time is of the essence, then the grey dries much more quickly.

Lorena, Texas (South of Waco)

Question answered. Thank You. I am in no hurry to put back in service so Black it is. Also going to use in place of side Seals.