Chevy-explain 1&2 piece oil seals?

[dudevato]

I read on sites about one and two piece oil seals when looking on line for small block Chevrolet engines. I'm thinkng this is refering to the rear seal? Only the rear? Did this change at some point in time, with maybe the early V8's having one kind, then the later years having the other? Is there an advantage to one or the other? Any and all info is welcome. Thanks for your time and knowledge? dudevato in southern california with a '75 Jaguar sedan / 350-350 and a darn hole in the oil pan, just about the size of a rod :eek:

[MI2600]

From '55 until about '86, the SBCs were two-piece rear seals. They went to the one-piece after that. The latter type eliminated chance of rear seal leaks.