Sorry to hear that. My 87 2.6 did the very same exact thing a couple months ago. The coolant leak you see is the running down the inside of the exhaust manifold.

My cylinder head (also from Clearwater with 90+ miles)developed a casting porosity leak in the #3 exhaust runner area. A porosity leak is a pin hole leak in the aluminum casting.

You MAYBE able at remove the exhaust manifold and closely look at the walls of the exhaust runners to spot the leak. The coolant will "steam clean" area around downstream of the leak.Hopefully some else has a better idea.

As a temporary fix I used GM coolant system leak sealer tablets to stop up the leak till I could schedule some downtime to replace head. Please Google "gm coolant seal leak tablet" for part numbers and more info.
When I posted about my leak someone else replied back they had the same exact issue.Please use search function to find the post if interested.

Good luck and hope you do not have to warranty out your Clearwater head. Also if your head is defective it isolated and not widespread problem.
Again good luck and hope its not the head....If its the head I hope Clearwater stands behind their warranty