Oil cooler failure??

Hey guys, I've just found oil in my radiator and am about tu start pulling the engine apart to do the head gasket but suspect the oil cooler may be the culprit.
I'm way out of my depth here, but ive done most things on the car over the years so gonna have a go at this.
The water jacket got a hairline crack at a bolt years ago which I bogged and a few months back that blew off and the crack became a hole which I bogged again. It's had a tiny leak which results in me topping up the radiator every 3 days, so on discovering oil in the radiator I know I've caught it quickly as I've done minimal driving the last 2 days.
My understanding is that due to this small leak, my cooling system doesn't hold pressure when switched off so I believe no water has gotten into the engine as it doesn't look milky.
I've cleaned the whole engine bay and am about to start dismantling but am wondering if there are any diagnostics I can do while she is still able to run?
Also, I can't seem to find any info on a catastrophic failure with the oil cooler. Given it has sustained damage on the eater jacket I feel it's likely there could be internal damage allowing the oil and water to mix. So I'm hoping it's just that and not the head gasket or worse.
Any info would be immensely appreciated. Thanks heaps in advance!