78 automatic rear transmission seal leak

I have a 78 with an automatic transmission. The rear transmission seal is leaking a bit and was wondering what the typical cost is to replace the rear seal and-or if this is something I could do myself?
I do not have a lift but do have some floor jacks. I have done engine workd and brake work but nothing with the transmission before. Thanks Tom
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shaft, pull the seal and install new one, just a lip seal. Pay attention to the wear on the yoke, if the wear is deep you may need to replace it for the seal to fix the problem. GM number 24204540 seal cost about $5. Can't confirm that as being the correct number, old book, but the prices shouldn't be allot more. Wouldn't hurt to check those u'joints while the shaft is out.
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I think you have the THM 350, small shaft, 1.5 I.D.X 2.38 O.D. BCA (National) Part # 9613S $1.95 the bigger shaft is 1.89 I.D. THM 400.
Forgot to tell you that you will get some fluid when you pull the shaft.
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