Eureka, I believe we are coming to an end here!
Thanks to Matti's second photo it is clear now how the dipstick tube is fixed in place.
It starts with the bracket that is screwed onto the engine block behind the black holder for the steering pump fluid reservoir.
The bracket part number is: 130 010 00 40 and it is on all M130.983 engines starting with engine (manual transmission) # 005053 or engine #008202 (automatic transmission).
It is shown as # 80 in my first attached picture below.
SLS sells as item # 218288 at 26,18€ and it looks like this:
There are two pipes attached to this bracket, the oil cooler line and the dipstick tube and both with clamp # 187 925 00 37. It is shown as # 81 in the picture. SLS sells it as item # 254069 at 3,45€ and it looks like this:
Sine the dipstick tube diameter is smaller it needs a rubber hose p/n 621 997 04 82 to fill the gap. It is shown as #85 in my picture.
SLS shows it as item # 207098 but NLA and it looks like this:
The two clamps around the pipes use the same screw and lock washer. The part numbers and the part drawing in my picture are from the s.p.l. #10180 for the M180 engine.
Anyone out there who can see a fly in the ointment?