Thanks guys for the suggestions. My w124 wagon has those rubber protector strips on the roof of the car, so I have never used my crossbars when transporting 10-20 2x4s from the lumber yard. But my w210 does not have anything on the roof other than the side rails of the MB roof rack. So I had planned to leave the cross bars on the car at all times, so that, without advanced planning, I could put something on the rack without it actually scratching the roof paint. I don't do a lot of highway driving these days, so the fuel economy hit wouldn't be big. I know they aren't supposed to actually hold a load, but they are actually pretty stout pieces of metal. I bet they could support 100-200 pounds if it was distributed like pieces of wood. But yes, for a kayak or bike rack, quality aftermarket crossbars would be necessary. Thanks again.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Removable cross bars are extremely versatile. In my opinion they're a much better solution than the rubber strips on the 124 wagon or those permanent factory cross bars. You can put them on and take them off in about 5 minutes and store them in the trunk of the wagon when not in use. Or you could slide then all the way to the back of the roof to minimize noise.

This is a pair of cheap generic cargoloc cross bars.
https://i.imgur.com/bBG3mqB.jpg

I use yakima round bars with my roof box.
https://i.imgur.com/hkFZ5wT.jpg

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CENSORED due to not family friendly words