It turns out my Goodwrench 350 is a 2-piece rear main seal.

[Blue85]

When I bought this Jimmy in 2000, I was told the engine was installed in the last 6 months. It was very clean, so this all tracked. My research many years ago said these were all 1-piece, so that's what I ordered. Now that it's apart I find sources saying these were all built in Mexico through the end of the 90's as the older 2-piece design.

I've been meaning to replace it for like 6 years and this means I could have done it with the transmission in place. However, looking at it without the flexplate, the rear main is fine and all/most of the leaking is from the oil pan gasket. Look at the dry mud right above the crank.

 

[Blue85]

For sale:

 

[Chevy305]

Interesting, do you have the center bolt valve covers?

 

[Blue85]

Perimeter bolt valve covers, 4-bolt main caps. I think they were always that way, at least until GM re-tooled several years ago and the prices went from like $2k to $5k. Some sites still list perimeter bolt Goodwrench engines: https://www.crateenginedepot.com/57-Ltr-350-CID-GM-Engine-1971-1985-New-12681429-2538-S-P9447.aspx.

It looks like the 2-piece seal never went away on these, even though I read somewhere that everything made after like 1987 was 1-piece.

 

[imiceman44]

Perimeter bolt valve covers, 4-bolt main caps. I think they were always that way, at least until GM re-tooled several years ago and the prices went from like $2k to $5k. Some sites still list perimeter bolt Goodwrench engines: https://www.crateenginedepot.com/57-Ltr-350-CID-GM-Engine-1971-1985-New-12681429-2538-S-P9447.aspx.

It looks like the 2-piece seal never went away on these, even though I read somewhere that everything made after like 1987 was 1-piece.

Everything that was offered in the cars after 87.
But stock left over had to be sold.
Plus I bet you the tooling in Mexico is still being used to make more, as long as it's good enough they keep using it.

 

[HankScorpio]

I have a "hecho en mexico" 350 with the 2 piece seal and perimeter valve cover bolts. It was purchased in 1995 from GM as a replacement for a 1982 truck. It was pretty durable, I put a lot of miles on it until the rest of the truck fell apart and rusted away.

 

[cheavyk10]

I've got a GM performance parts 350 "300hp" crate motor with a two-piece rear main seal and perimeter bolt valve covers I purchased in 2018, also made in Mexico. I think it was like $2,400 back then (and completely brand-new). It came with the old school 222 duration 114 lobe separation "327" cam. Needs some better heads and a bump up in compression, although it still runs really good.