88 C4 Leaking Tranny - Rear Yoke?

I've brought my car back to a reputable tranny shop twice now to seal tranny leaks. Finally stopped leaking except in the rear. Tranny guy tells me
that the rear trasmission seal is leaking and that he has to replace the whole rear yoke assembly? Replacing the seal didn't stop it. Does this make sence? is this a common prob with turbo 700r trans..? I don't think he's charging me for the labor to tear it down again but he's talking between $250 - $800. for a used/new yoke assembly?
Sorry about the flood of posts. I haven't been on here in awhile. Didn't use my vette for a few years due to financial constraints.
I used to get great advise from this group back in the day. Hoping someone will take the time to respond :)
Cheers!
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There is only 2 things that allow a seal to leak, the seal its self and the surface it is sealing on. If you have been around the Corvette groups very long you have seen the problems with brake seals, same problem. Rust. The yoke is cast iron and is polished by the seal when driven. Since it works in and out as well as around it can be left set with bright polished cast iron exposed to allow rust to form. Next time you drive it the rust becomes a rasp and eats your seal leaving some rust in the seal to eat the yoke. At some point even a new seal will not seal a yoke with a ring cut in it from the previous seals. Some repair shops have the ability to sleeve the yoke, most don't and/or choose to replace it; but either way it needs to have a good sealing surface. Is it common? Yes, for cars that sit for long periods of time regardless of the transmission type. As for the brake seals they just trap the moisture under the seal a eat the sealing surface. Very good reason to flush the brake system as required for its type of use.
As far as you injector problems, when were the cleaned last?
--
Dad
05 C6 Silver/Red 6spd Z51
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I agree with Dad, except for

There is a product called a speedy sleeve that can be purchased from any good industrial bearing and seal supplier. They do not require any special tools or presses and are simple to install with only a hammer. These sleeves are very thin and can be used with the stock seal size. They have a very smooth surface and are commonly used to repair yokes that are badly grooved under the seal. IIRC they are stainless and less inclined to rust than the stock yoke.
Most seals seep enough that rust is not a problem and is a good reason not to pressure wash close to any seal as this not only removes the oil but can also drive dirt and moisture under the seal.
If the splines on the inside of the yoke are worn then the only solution is a new yoke but they are not expensive, IIRC $50-75 but YMMV. I suspect that the yokes are a common GM part used in many applications but YMMV. I also suspect that GM is the best source for new yokes but again YMMV.
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Hey Dad. How long have you been hanging around here? I remember you from YEARS ago! Cheers! I used a can of something or other a couple years ago which wold mean maybe 1000k. Thanks for the advice. Appreciate it. I'll check with my tranny guy. Dropping it off tomorrow to have him look at it. He doesn't recall if he replaced teh seal or not.

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'86 Any special tools needed to replace trans seal and filter kit? how many pints of fluid needed? any tricks to be aware of. i'm in awe of the guy who did this every year. get fluid and kit at Chevy store or Parts place?
ssome ?

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