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The best rope seal unfortunately is not made any more.
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He's referring to the "BEST" brand graphite woven rope rear main seals, not which type of material the seal is made from. The "BEST" seals are still being made and sold currently, for Pontiac and other engines which used the older design rope seals.
Link to "BEST" brand graphite woven rear main seal, which has shown to be as effective as the old asbestos rope seals which the feds outlawed years ago. Much better results than the fiberglass seals that replaced the asbestos rope.
https://www.ebay.com/itm/27678390213...4f286bc67173dd
Any rear seal can leak if not installed correctly. Rope, 1 piece neoprene, 2 piece neoprene. You have to take time when doing it, and follow the directions. Even if you follow directions to the Tee, they can still leak, been there done that.
Personally I've done dozens of Pontiac as well as other brands of rope seals. The only way I've never had any luck doing the procedure, is packing the old upper half in the block with the crank still in the block, then inserting short pieces on both ends. Every time I've tried this procedure in chassis from under the car, they have leaked. GM has this procedure in their shop manuals, but I've never done one this way and had it seal.
Pull the engine and replace both halves by lifting the crank out of the block if you want any chance at all of sealing the rope style seals. I've had zero success with repacking in chassis repairs. I've also tried Chinese fingers to pull a new rope seal into the upper block groove, waste of time, never sealed properly because you're actually stretching the seal, instead of packing it more densely.
I've never had the Kent Moore packing tool to use, I use whatever I can find that is the approximate same diameter as the seal surface on the crank to pack it into the cap. I usually pack both halves separately into the main seal cap, then transfer one to the block groove. I trim the ends of the upper seal after it's bedded into the block.
The main bearing journal isn't the same size as the section that the seal rides on. The seal surface behind the slinger ring is maybe 1/8-1/4 inch larger than the bearing surface is.
I.E. a 3 inch main journal will have a seal surface 3 1/8 - 3 1/4 inches in diameter.
I've also used an old junk crankshaft and driven the cap onto the old crank to form them into the groove, but of course you need a spare junk core to be able to do that.
Good luck in whatever you decide to do, because Pontiac rear mains can be very challenging to seal completely dry. Most garages won't even give you an estimate on resealing one, and if they do, they may not warranty the labor if it leaks. They don't want the liability, and grief that goes along with it. Doing the job the second time for free isn't a good business model for profit making.