Testing td5 Oil Cooler

I had the dreaded oil in coolant problem and have taken the 110 to the garage and asked them to swap it out if that's indeed the issue. How would they/I go about testing the oil cooler once it's out?

The oil cooler can be pressure tested under water and will show bubbles if its leaking.

Thanks shifty!

Nextg question: How do I get the gunge out of my cooling system? It's all throughout....Previously I just unscrewed the coolant drain plug next to the rad, then took the pipe from the header tank and whacked it on my hose and turned it right up - it fired loads of gunk out but presumably this won't shift the stuff in the radiator unless the thermostat was open?