I have a low mileage 72 trans ( 6000mi. ) that I'm converting to a side shifter. It has a front seal that is very different from the one in the 74 trans that is being used for linkage parts. The black seal in the 74 trans is usually what is found on all the cases I've dismantled. . The sealing area on the blue 72 is inset much deeper into the case and the outer surface sits a machined area not used on the 74 black seal. I'm sure the 72 trans has never been apart so it's an original piece. So, should I knock it out and use the seal that is in the gasket set?

Also got to say that it's great to take a trans apart and see everything inside looks like new!

I doubt either are original seals. The blue seal is not original, it is a common aftermarket seal, I use to see them all the time.
The blue seal does not have the outer dust seal like the black seal has but the oil seal lip on both seals probably ride very close to the same place on the shaft.
Typically the seals have a size imbosed on them which is a set of 3 - 2digit numbers for inner diameter, outer diameter and thickness (probably not in that order) so you should be able to determine the size of the sealk you need to get to replace the one in question.

Jim

Contact Dr. Evel.

To do the side shift conversion you already have it pretty much apart. So I would go ahead and replace this seal (along with the others). You will find some seals that are "T" shaped (like the blue one) in that as you seat them, they will only go so far in before the top of the "T" makes contact. Most are like the black one in that they don't have the "T" top and you can accidentally push them straight through. However you do need to make sure they are deep enough that the throw-out bearing guide does not touch them. Both look to be seated correctly, but they are just different styles.

The other item of note is that your input shaft is a bit rusty. When you put in the new seal you will want to ensure that the part of the seal that rides on the shaft touches in the same location as the old. If it rides on that rusty area, you will wear it out. I would clean, polish and oil that part of the input shaft to help reduce the risk of that being an issue in the future.

Richard

The blue seal is an early version, used on 356s and VWs. The black seal without an outer lip is the updated version. It is of a double inner lip design, and much better in terms of efficiency and longevity. If the blue seal is old, I would replace it. if not, you could probably save a few bucks and leave it in. I wouldn't, but that's just how I am.

The Cap'n

I polished the input shaft and will pop out that blue seal in the morning. A black one came with the gasket set and I'll install that. Also going to replace all the gaskets and seals. Trans has very few miles on it but has been setting around for almost forty years.

Be careful to not scratch the bore in the case when you remove the seal. If the case is still apart you can tap it out from the inside. If the transmission is still together you can use a seal puller, or screw a small screw into the seal and use that to pull it out. Those seals fit tightly. I lubricate mine when I install them and as it's easy to tear them if you are not careful.

Richard

Thanks for the info. It is still apart and I'll pop the seal out from the inside. Will also lube it up before installing it. Thanks, Ray