M880 transmission seals?

[J2H]

I am looking at a 77 M880 and the owner says the rear transmission seal needs to be replaced as it leaks some trans fluid... how much do these run? Easy to put on and take off?

 

[Bob H]

seller likely refering to t-case rear seal.
all std 77 Dodge truck stuff, any trans shop can deal with.

 

[J2H]

How much do you think that might run?