2001, coolant overflow question

My temp gauge was only reading 1/4 for the last couple of months. I constantly checked the coolant overflow and it was always good. The other day, the check overflow light came on and when I check it, it was empty! I filled it up and noticed there were drops coming out the bottom of the engine.

Took it to the shop, they said the thermostat was bad (it was changed once about 3 years ago) and that caused the engine to run hot on one side (??), whiched caused exess heat to go to the overflow, causing the seals to not "seal" right, causing leakage.

They changed the thermostat and said they repaired the overflow with some sort of bond stuff. He said he would prefer to replace it, but I thought we would see how it ran first.

The next day, after driving for a while, the temp guage reads just short of 1/2, where it should, and then the check fluid light came on. I checked and no water/coolant in the overflow. I filled it up and there's a much bigger drippage now than before.

My question, can I use a generic overflow for this car or do I have to get one that fits properly? I hate to bring it back to that shop when I can do it myself, but I can't find one that fits unless I go to the dealer. I just get a generic from NAPA if I can.

Any advice would be great. Thanks

www.car-parts.com (used)

www.gmpartsdirect.com

Salvage yards are also a good option.

I honestly dont see a reason why a generic one wouldnt work.