O2 sensor shorting intermittently
 

My 88 300CE was having problems passing the emmission testing,I replaced the O2 sensor and it still failed,just.
I replaced the plugs and it didn't make much difference,failed again.I took the car into a local shop,they said it was my injectors.When we picked the car up they said the O2 sensor I installed was shorting and they replaced it.The part was a different number than the one they originally said it needed as well as the one I replaced from the MB dealer.
The sensor I bought at the dealer was Bosch #13925,the one they installed was Bosch # 13130.Are they the same part with a different number?Is there a way to bench-test the 'bad' one?Hopefully the dealer will take it back,or else I'm out $180.I hope someone can help,thanks in advance.