The brakes seem to work fine and I can find no leaks, but the pedal is very low. I think maybe I got air in the system as the fluid level was down but not sure.

The symptom is, brake starts to work at the very same place as before but sinks slowly and gets hard near the bottom. pumping it a time or two brings it back up and then it doesn't sink any more. Also, with the engine off, same symptoms, you just have to push a lot harder. The brake fluid is not going down and just now looking at the MC, I don't think the fluid level was anywhere near low.

Was going to buy a master cylinder but O'Rielly's does not know the P/N, or more correctly they show 2 different one, one with Stability Control and one without. Did an SS have stability control?

Annoyingly Chevy discontinued it. NAPA can get one tomorrow, O'Reilly's today at 5 and Autozone put me on infinite hold.

 

Part numbers be very careful as some are sure they’re gonna fit, but notice some say with or without certain opinions
Cheaper are not really worth the aggravation for the price

https://www.rockauto.com/en/catalog/chevrolet,2008

 

Yes, but how do I know which one to order? Looks like the difference might be two 12mm ports vs one 12mm and one 10mm. What does an SS need?

 

Low fluid means bad disc pads, unless there is a leak. You should never "top off" the brake fluid because it is a measure of disc brake pad wear.
If you have a ESC button you have Stability control.

 

OK, but I need to fix the problem, does it sound like a bad master cylinder?
How do I know what master cylinder to buy?
Does an 2008 SS Automatic have stability Control?

I'm not used to calling a parts store and having them say, we don't know what part you need.

 

How old are your pad pads? Your front rotors? How about the flexible hoses, are they swollen?

 

I'll check the pads and hoses after I fix this problem. Pads can't cause this problem and likely neither will a hose. The front hoses are newish, the rears are original. I ordered a new MC from NAPA and it will be here tomorrow.

 

Hope you fine the problem.

 

Please ignore my statement that low fluid is an indicator of worn brake pads, and yjat if you have an ESC.Traction button you have stability control.

 

So I gave up. I followed the page in the manual showing how to remove the fuse block and supports and even looking at the manual page, could not find the nuts it claimed were there. I pulled the 4 bolts and the battery cables and then the top came off, but the next piece did not want to come out and the nut and bolt it showed did not seem to be there. I miss working on old cars where things were actually accessible. Tomorrow it goes to the shop to let them try.