The only way to really know for sure is replace them and see if the code comes back.
I think code 45 is a rich exhaust code however (someone correct me if I am mistaken). Usually if you get a code like that, it means the sensor is working.
If you have a 307, you could easily have a carb problem that is giving you a rich mixture and setting codes.
The only way to really know is to monitor the O2 sensor reading on a scan tool and force the system rich or lean and see if the reading follows the condition you are inducing.
Some of those older cars are pretty hard to diagnose without a lot of special equipment.
There's a test procedure for the O2 sensor in the service manual.
It's more than likely the carburetor on that engine that's giving you problems though. Check and make sure that whole vacuum nightmare under the hood is connected and not leaking. About 80 lines run, in some way, to the MAP sensor. If they're bad, you'll definitely run rich.
Got a high impedance volt meter? Must be digital or tubes (VTVM).
If not, do NOT connect up anything to the O2 line.
95% of the time O2 sensors are not bad. They get fouled or poisoned, but rarely ever go bad, even over a lifetime.
Often another problem will make them lazy or read off, but correct that problem, get it hot, and often it will clear up and start to work again.
Code 45 is rich condition: Test description: 1.) Code 45 is set when the O2 sensor signal voltage remains above .7 volts for 30 seconds or more and in "closed loop". 2.) Engine time after start is one minute or more. 3.) Throttle position between 2 % and 20 %.
(stolen graciously from http://www.misterfixit.com/code45.htm)
so evaluate what could make the exhaust rich, don't mess with the messenger, (the O2), mess with what would make it rich. Air filter, carb, float, fuel pump, PCV, charcoal vapor canister, bad or disconnected MAP sensor, etc.
How do ya tell it your 02 sensors bad or not? My 87 Brougham 307 gives me a code 45, but I'm not sure its correct.
Often O2 sensors are replaced with inferior aftermarket units and they go bad after a year or so. I know, I did this on my '86 with a Niehoff and the fuel economy went into the toilet after a year. I replaced it with a Delco and all was well again.
O2 sensors do go bad after time, as the result of contamination and such, and I find that it is good practice to replace them peridically. They are not expensive (compared to some of the 3-wire jobs) It can make a differance in driveability and fuel economy.
Advice I had from Scott Mueller was only use Delco sensors. I have used a Bosch, which seemed ok. But I have only replaced 1, and that was the dealer doing it, but I had them give me the old one back, which wasn't bad afterall. Love ~trustworthy~ dealers... A guess that it should be bad is reasonable, a cracked sparkplug wire arced to the sensor and blew that A/D on the computer, so the O2 sensor was dead to the Scan Tool. BUT, to blindly replace it was irresponsible. But I was a Spec4 in the Army and left the next day to go back to Colorado, so I didn't have time to fight them on it.
Make sure the M/C (Mixture Control) solenoid is working, that is a sure sign that something is wrong, if you stall the engine (like close the choke on it when it is idling) the solenoid should click for a few seconds after it stalls. It WILL set some codes when you do that, but they should clear once it is started and run again. You can pull battery to clear too.