I have just ordered the feedback pot for my airflow meter ('91 190E 2.3) from a place that sells Bosch generic parts. A source was listed previously in Russia, but giving out my CC# to them was not for me. This location is in VA, and I'll report back how the transaction goes. Price is $71 with $9 shipping, and tax if in VA:

https://www.olyonline.com

BTW, the part# for mine is 3437 224 035, which is the same as someone listed for a W124 engine - but I don't recall which one.

Steve