2006 Chevy Impala Coolant smell

Had thermostat replaced 3 months ago. Had to continue to add coolant (over a week's time) until resivoir was filled between "low" and "full" when at operating temp. Also purged air from system.

I smell warm coolant outside of car after a short trip. Under hood, smell is strong around filler cap area. There are no leaks onto the driveway nor any wet areas around hose connections or water pump housing. Had to add about 8 ounces of coolant recently to bring resivor back to proper level.
Found sticky accumulation of coolant in detent of water pump casting below and slightly to right of power steering pully. This is a very small, slow leak. Can't find source

Suggestions?