Transmsiion cooler coolant leak

[BettyMini]

2008 Cooper. Az car. Seen from underneath, my mechanic showed me coolant dripping off the transmission oil cooler. He said the cooler needs to be replaced. Expensive part, big labor bill. I was able to view ithe cooler from above and confirmed that neither of the coolant hoses is leaking. From a Clinton manual I understand that there are two o-rings, but I would guess that they seal in transmission oil. Is anyone aware of one of these coolers springing a coolant leak from the body of the cooler? If it is not the cooler leaking, is there a common leak in this vicinity?