Ok - thanks for the info. I'll pass it on to the shop to see what they say.

Yep, sounds like a good 'ol fashioned cold leak. Hoses will become brittle and adapt less to temp changes and clamps do vibrate loose. Check the connection of the lower radiator hose to the block. Bet you will find the culprit right there. Worse case would be the water pump doing a cold leak, like already mentioned, due to seal hardening. I have had both issues in the past.