I have a 2013 Silverado 1500 Ext. cab. Where the cab mounts to the frame on the rear driver side, the bolt is constantly damp with antifreeze (I had our chemist at work test it). Took it in and the dealer pressure tested the system and it passed, but I still get the spot on my garage floor daily. Any advice I could take back to them would be appreciated, unless this is a first. Thanks

 

Heater core leaking inside? Is the carpet wet?

 

IF the system really pressure tested good, then it might also be the overflow tank leaking, but that is on the passenger side of the vehicle for GMT900....
I would go with Richardx2 suggestion and investigate the top side of that area... but do check the over flow tube of the tank and make sure its not running down the frame and finally dripping at your bolt point...

 

No wet carpet, thanks. Thinking it maybe following the frame back????

 

They pumped it up to 30 psi for 30 minutes and it held. As slow of drip it is, maybe this wasn't long enough to show. Where the drip shows, maybe it's following the frame back. Seems it's more obvious after a half hour plus drive and I see it the following morning...nothing immediate. Thanks and keep thinking...I am.