I would appreciate some thoughts on this prior to making the trek to Dealer so I can be somewhat prepared. 2002 DHS, 71,000 miles. Just noticed what I think is a small pool of transmission fluid on floor when driving into garage last night. It is located on drivers side about middle of transmission. [I still have to verify that it is not the orange dex cool.] I add the latter because while out last night the add coolant message also appeared.
If it is transmission fluid I assume this is something that others have experienced and would appreciate any thoughts on why and about how much repair cost would be anticipated. Is it the type repair that can be handled by non dealer mechanic?

Since you noticed a pool of fluid and had the check coolant level at the same time, I would think it is coolant and start looking for cooling system leaks but, verify the fluid to be sure.

This happened to me this summer and it was the water pump. My coolant resavior was empty. We had it repaired at a non dealer shop, don't remember how much but not out of sight.