First off I'm a new member, just purchased a 1951 3100, and have my first question. The rear seal on my transmission is leaking at the yoke input, and I'd like to ID my transmission so the correct seal can be purchased. It's a 3sp manual, iron case, open shaft. A quick check on another website shows it matching to a Saginaw (7 bolt cover, reverse on the case not tail housing). The numbers are as follows:

Drivers side case : GM3 3858992 (2 is badly worn)
186
Pass side case : GM1 3858998
C116
Pass tail housing : GM14

Photos can be provided if necessary. The trans may or may not be original. The truck has been modified in other areas. I just need to ID the make and model of the trans so the correct part can be purchased. I don't really need to know about ratios, etc. at this point. Maybe all tail shaft seals are the same (doubtful)?

Thank you in advance. I look forward to expanding my knowledge through this website!