Mike is right...rare for it to be the timing cover gasket......sure it wasn't the waterpump gasket or the water pump weep hole?

Did you try to find the leak(before you pulled the pump off), by pressure testing the system, with a coolant pressure tester on the radiator?

I found this post by REGAL GUY it shows how the cover can corrode on one side. From what REGAL GUY said not enough threads on some of the bolts to clamp it down proper
https://www.gmforum.com/buick-172/gm...ess-up-308164/

I forgot, we are dealing with a 2006+ Series 3 engines. I'm not familiar with the changes from 2005 Series 2 to 2006+Series 3 engines. So, I'll rephrase my previous statement, I've never seen a Series 2 leak from behind the water pump.

It looks like a common problem now from REGAL GUYS write up.

Was there corrosion on the left side of the timing cover ?

the problem was the timing cover gasket. which was 90 bucks. i had to take it to a mechanic. ended up costing 700 including a new water pump