Broken Thermostat Housing Bolt (Please Help!)
 

I have a 2007 Cadillac STS 3.6l. I have been attempting to change my thermostat and I discovered a bolt has broken in my thermostat housing. I have tried several methods to remove it, vice grips, the drill bit bolt removal tool from Autozone. I have no idea how to remove it and I need some help. I unfortunately have no welding experience. Is it easier to attempt to remove the whole part the bot is in? I am not an experienced mechanic so any help would be greatly appreciated. This is my first post in these forums so thank you in advance.

Well, I just took the whole part off. It's GM part number 12597255, the engine coolant thermostat housing. Under the GM 12597255 on the part it also says "W100.2". Can anyone tell me what that number with the W is? Thank you in advance.

https://cimg4.ibsrv.net/gimg/www.cad...d9bad2799e.jpg
Does anyone know what the "W100.2" is? I found the same part online but the W number is not the same.