Anyone ever replaced the auto. tranny servo o ring?

It seems to be leaking around there again. 18 months ago the tranny was leaking bad and on the invoice it says they replace the servo O-ring for $45. It seems to be leaking not as bad from the same place. I did have it rebuilt at another place last Dec. but the owner either retired or relocated. Trying to hunt him down to avoid going to the more expensive place in town. It has been fine since they rebuilt it.
Thought I could try it myself cheaper if there are no pandora boxes to it.

Thanks......