Are you sure that it was an OEM part? Cheap O2 sensors are all over the place. I don't trust anything that comes out of eBay. If you said you got it from Pelican Parts then it is worth comparing. Look up the same part on Mercedes of Atlanta web page to get the correct dealer pricing. And I don't begrudge the dealer his costs because of his overhead. Having said that, I go to an independent.

Anziani
'97 CL600 56K

I realize this is an old thread and I only read the first and last post.

The Op and those that agree with him need to do the following when repairing their own car:

Call off work and take unpaid time off for all activities related to the repair.

Keep a stock of parts on hand for various cars in the hopes that one comes in that needs that specific part.

Breakdown the cost of commercial insurance for the facility you are working in and apply that to the cost of repair.

Purchase and maintain an extensive assortment of specialty tools. Make sure you can service every car back to at least 1980 otherwise you will suffer the wrath of this guy in post 46 _expecting_ a MB dealer to have specialized tooling to fix his 1980 car. http://www.peachparts.com/shopforum/diesel-discussion/377119-shops-useless-these-days-4.html

Pay for all utilities associated with the facility you are working in.

Add in any other expense related to the repair, this total is the true cost of repair less any sort of profit.

After the job is done, be sure to call up the local restaurant and tell them you can get what they have on the menu for 20% of what they are charging at a grocery store and see how far that gets you.

You nailed it 97SL320! The independents are sort of in a time warp. After they quit Mercedes they knew everything about a range of cars. The longer they stay independent the less they know about the newer models. My mechanic is a perfect fit for me as he quit about the time my car came on the market. He didn't have much experience with the 120 engine but we took a long, hard look at it and realized it was nothing but TWO 6 bangers on a common crank. We have had no troubles at all with the car except room to work.
Anziani
'97 CL600 56K