Agreed with mdonohue05 - I have used new rope seals, new BEST seals and NOS asbestos seals and the NOS seals work the "best" followed by the "BEST" brand seals if you are using sticking with the original rope design.
The new split rubber lip seals are easy to install and if you clean the mating surfaces well and put a small micro-dab of silicone sealant on the ends where they meet . . .
If you are sold on going with a rope seal - the only way to do this well is to remove the crankshaft. You cannot effectively pack enough of the seal into the block cavity with the crank in the way.
I have just over 2000 miles on my last NOS rope seal in a GMC 270 and nary a drop (and yes, the crankcase is full of oil)
