2001 Oldsmobile Aurora Coolant Surge Tank

Engine Cooling problem
2001 Oldsmobile Aurora Two Wheel Drive Automatic 32000 miles

I have a leak somewhere which drops coolant often. The dealer where I purchased same could not find the leak (did the pressure test). Is there something we are missing in trying to locate the leak? Could it be a nut & bolt problem - not tight enough? Please advise. Thank you. If you can pin point and direct me to a reputable place for service, I will gladly give a donation, but until I get some sort of legit info, I will not donate. This is the first time that I've tried soliciting over the internet.