Dealt with a similar issue on my old 06 Z71 before it was totaled. Gonna say it’s your water pump weep hole, all of the coolant would seep down and drip behind the pan. Literally just had this job done 3 months ago (2 weeks before my wreck...) change out the water pump ($110 on Amazon & $200 in labor if you don’t do it yourself) and you should be good.Got a message on the DIC "Low Coolant". It has 290k miles. WP replaced around 150k miles. Radiator, hoses and connectors are original. Reservoir level is very low. I saw coolant dripping at the back of the engine oil pan under cover. Probably dripping on the under cover and running down the back.
I'm going to park it for a while until I can find time to investigate as I am going out of town for a few weeks.
Hope this helps man!