Oil cooler leak
 

After pulling my transmission I saw a lot of oily dirty accumulated on the boss that runs downwards from the oil cooler on the lhs of the engine. I cleaned it up but wonder what typical failure modes are for the cooler? I am guessing the o-rings can fail after 18 years.
Any inputs appreciated. The oil was dry so obviously old. The bottom of the plastic inlet tract was filthy too

It could obviously become simply loose and leak. When I did WP, thermo, flush, I also replaced the 'O' rings. The originals where some what flattened and hard after 13 years. So I would imagine in that state, it would take very little to start a leak.
So I had no coolant or oil when I did mine but the cooler/heat exchanger still had coolant and oil inside