I would try changing tranny fluid. Haynes manual recomends every2 yrs or 24,000 miles. Based off the car not moving forwards when releasing brake pedal n in gear. I changed the tranny fluid in my 99 camaro at 63,000 n the amount of crap in the pan was terrible! Ur cobalt is similar just smaller pan. costs $50 at most for fluid,gasket,filter n rtv. just have an accurate tourque wrench for re install. if bolts r too tight it leaks or too loose. Just get a jack,jack stands, n set aside a few hours.
2005 COBALT BASE 2.2 AUTO ARRIVAL BLUE:SOLD
2008 PONTIAC G5 2.2 AUTO SLATE METALLIC:SOLD
1999 CHEVY CAMARO 3800 AUTO HUGGER ORANGE
2009 COBALT LS XFE 5SPD VICTORY RED