Apologies if this has been discussed a thousand times before and there's a thread on this site, but...

The advanced key door locking/unlocking on my A4 has gone down for the fourth time, I'm now out of warranty and the dealer wants $450 to fix it. He already charged me $115 to diagnose it. This time, I'm gonna fix it myself.

I know that the driver's door sensor is down, and I've trawled the web for how to fix it, but my question is about the part number. For this vehicle, should I use:
A4G8 927 753, or
A4G8 927 753 A

Also, these parts are available on Ebay at much less than Audi ($~$20 versus ~$95). The parts are from China, but have the four rings and the part number on them, so they look legit. Anyone had experience with these? I'm tempted to try them because they can't be any less reliable than the genuine parts!