I checked on the part availability and it costs approx. USD250. But you know what? The dealer REFUSED to sell it to me. He said the part is not suitable for a W126, and will not work.
"Too complicated", he says.
What a cheek.
I described the process as outlined by MBenz, and he insisted it won't work and proceeded to put the part back on the shelf. He then sat down at the desk looking at me as if to say "what else do you want?".
I walked away, thinking of another dealier. But I don't know of any other than him.