1 lip or 2 lip Rear Main Seal?

[Driftwood]

Which should I use for my '69 350/350? I've received advice both ways, and also been told either will work. Any recommendations are appreciated. Thanks.

 

[ChuckG]

Conventional wisdom says use the 2 lip seal. Why? The original one piece seal can wear a slight groove in the crank. The "2 lipper" will straddle that area, and create a better seal on a "fresh" area of the crank. Chuck