Oil cooler leak

[Nedlands]

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

[kk2002s]

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