Tranny Line Leak?

[uchi]

I was looking the block heater the other night and noticed a thin line on the pass side going intothe rad wad slowly leaking. Not alot but enough to leave a greasy spot on the support below it and the line has fluid on it. It was dark and the fluid was dirty so I couldnt tell what it was. I know Gm in the past has had tranny coolers built into the rad. Just making sure thats whats leaking. Thin rubber line that goes to a metal line pass side top of the rad