Lamba Sensors

[samastonlongley]

My 4.3 Vantage has been flashing up a slow response from the Lamba sensors and subsequently trigger the engine management light. I've plugged the code reader in and it's coming up that both are at fault giving a 'slow response'. I know this is a fairly common on the 4.3's my car was previously owned in London and perhaps its not adjusting well to the North Yorkshire Moors😉
What I'm wondering is has anyone replaced these before a aftermarket version like a bosch version for example? As the AM dealer seem to be quoting me there usual expensive prices. Any help greatly appreciated!