Hi guys -- Well, I discovered that when I replaced the manifold gaskets last winter, I bought the aluminum elbow set, and the o-ring on the large elbow coming out of the water pump was bad. That must have been the source of the leak. Had I used a mirror, I should have been able to see the coolant coming out.
I mistakenly bought the $45 GOPLUS radiator leak kit, only to find it didn't include an adapter for GM or Ford radiators! Sent it back, which cost me $20 for shipping. In looking more closely this time, I find the complete package for adapting to a GM radiator is quite expensive. O'Reilly rents a tester for apparently no cost. What would you recommend? Thanks for everyone'* help. --- Rework