2011 Enclave cooling issue - what do you think?

I have a 2011 Buick Enclave, few months ago I started noticing small drips of antifreeze underneath the car on the garage floor, I remove the front cover to access the radiator cap and saw the fluid was a little low so I filled it up, It's never gotten over 220 but every now and then I have to put a little more antifreeze in it. I took it to a local mechanic to see if they could locate a possible leak in the cooling system they could not find one, they told me that it was most likely the thermostat sticking pressure would build up and antifreeze would leak out of weepoles they claim it's a safety issue these engines have to keep them from building up too much pressure, they wanted $800 roughly to replace the thermostat I thought that was ridiculous. So I'm going to do it myself But my question is does anybody know if what they say is correct that if your thermostat is sticking and pressures building up that there's a place where antifreeze leaks out to help relieve that pressure. It's not leaking all the time just on occasion I'll find some in the garage floor after a nice long drive The heater in the car works fine The AC in the car works fine. I've looked all around the thermostat housing and have not located any leaks but as a precaution I'm going to change out the thermostat and the housing anyways. Any advice would be appreciated