[Newsguy]

Looking to tap into some collective wisdom here.
Picked up a 2002 S which had some poorly-executed repairs. Editing the story down, I elected to get another engine.
I replaced the IMS bearing and the RMS. It had a new oil cooler already.
It's in the car now, and after filling it with oil and started to refill coolant.
Last night, I found oil dripping from the bellhousing bottom. Today, I was resigned to taking the transmission out as I figured I didn't seat the seal well. So I started draining the oil to lower the level. I got a surprise in the form of coolant draining instead.
Now, is the obvious suspect the new intercooler? Or did this engine already likely have an intermix problem dumping gallons of coolant in the oil? Or am I an idiot and just plumbed wrong?
Thanks for any ideas.