This weekend's project is the front two oxygen sensors in my 540, it's been throwing CELs, and idling rough along with the light. Plus, I think they're original, and at 130k it's time anyway. Should I expect to partially drop the exhaust, or can I get to them without? Do I need to get the little sensor socket, or can I get a wrench or crow's foot on it? I just want to get prepared today, the dealership isn't open Saturdays if I end up needing exhaust gaskets.

As an aside, I found sensors at O'Reilly's for $52 each, they're the splice in type. They're Beck Arnley branded, but I'm not sure who makes the sensor. They have a number stamping on the hex section similar to many Bosch parts, makes me wonder. I've found lots of good stuff at O'Reilly's cheap, when I did the CV boots on my 951 the box was an off brand, but the boots were OE Lobro. Half the price I could get them for elsewhere.