AC 8050 oil in coolant

Each pair of engine oil cooler core Orings have a weep hole in the middle to signal to you the operator that there is a problem. Those holes should have been cleaned while the cooler was apart so they are open. If there's nothing coming out of either one, I wonder if you simply don't have residual oil in the cooling system making it's way to the radiator cap. Any amount of oil, even an ounce or two, will always make it to the top when the engine gets used. Cleaning of the cooling system requires using Dawn dish soap and straight water and flush/drain 2 or 3 or 4 times to get the majority of the oil removed. Overfilling the radiator when cold each morning will help vomit out any remaining oil when the coolant temp reaches normal. In short, I'm not sure you still have a problem, but residual oil.

I would suspect the head gasket.

Take thermostats out before trying to flush out.         MACK

I know, totally different animal but here is my experience with oil/coolant intermix on VW diesels

any time this would happen on those it would be the pressurized port in the block to the head that would lose it's seal. on those head gaskets there was a ring in the HG that would give up over time and allow oil to piss into the coolant. later cars would suffer (rare, but happened) from a bad oil cooler.

if you have the head off, I would have it checked out. no need to do the job x2. chances are it may need a slight clean up...or not but I wouldn't take the risk of just putting a gasket in there.

now, i'm not sure about your engine, I would assume it would be possible but I had one (vw diesel) that a HG didn't fix the issue. at a total loss, I had the head off, filled the block back up with coolant almost flush with the deck. I made a rig with my air gun to pressurize the oil by removing the sender. I hit it with shop air and watched the coolant bubble. turns out that engine was overheated real bad at one point and there was a crack somewhere in the block