Cotter pin in oil pan

[Bacchus]

Hey guys. Digging up this old thread.

I had my '40 flathead rebuilt last year. Ran it for a short period (like less than 30 minutes) and then set it in. Put the body on and got it home to the garage where it sat all winter.

About a month ago I come out and see a huge pool of oil on my floor. Roll it out, and it's coming from the cotter pin. What does this mean? Does this mean rear main seal is gone on my rebuilt engine?