First thing I would check is the overflow line (not exactly sure what it's called.) It is a little 3/8" plastic line that runs from the pump body to the top of the transmission. The get old and crack, sometimes a very small unnoticeable crack can cause a leak. Since 1985 we've had to replace that line twice on our 2550.
That's about the only easy one to check, if it isn't that it has to be at one of the seals or fittings.