Replacing differential Seal?

[Fiat88]

Gonna have my automatic trans rear output seal replaced, the guy quoted me $50-$75. I also noticed that I have a small differential leak but he didn't quote me a price for that because he has to see how it is situated. Before I order the seal, do you think that it will be an expensive job for the mechanic to do the diff seal? Is it a hard job? Thanks in advance!

[124JOE]

vandor posted a good bit of info on this
you can remove the pinion nut and replace the seal
when you go to put the nut back on you have to crush the sleave just a bit

or buy all new and do it by the book PIA