My emissions light

[Kingash]

Hi guys recently took the coupe into a specialist to find out what the actual reason was behind my emissions light as it has been on for a few weeks now, just havent had the time with work etc, turns out its the post cat lambda sensor cycl 4-6. Garage has quoted me £249 for the part from BMW themselves. Has anyone else had this problem and should i worry about getting it done straight away? any help is welcomed