Hello Cees and Naj,
I can shed some light on the subject. Mercedes published a service bulletin in June 1969.
It goes on to say "due to increased use of rock salt on highways during winter"......can cause start certain starting problems such as ignition cross-firing due to the formation of moisture and salt residue.
One measure taken to help the situation was the protective coverings added to the distributor inside and out, and the coil cover.
I do not know if these were added to all W113 cars after this time, or if they were added to the cars going to colder climates or certain countries.
My documentation goes on to explain that when the distributor boot is installed the ignition wires must be routed under the fuel injecion lines instead of on top. There are occasional glimpses of these "boots" in the BBB like on page 00-1/2 (fig.00-1/3).
In any case, these are somewhat rare these days since they are often removed and lost over the years. View the three piece set below.
Download Attachment: ignition covers 1.jpg56.8 KB
Download Attachment: ignition covers 2.jpg55.96 KB
The early version which is most correct for the W113 cars has the rarer metal snaps. The later version (Possibly after W113 production)had plastic snaps.
These covers are good waterproofing for owners who like to wash down their engines.
Joe Alexander
Blacklick, Ohio