In possibly concluding this thread, I have just finished rebuilding the fuel tank expansion system and the fuel venting system and thought it might be helpful to post a "how-to" for early W111 cars. I have a 111.023 Cabrio but this should apply to the early coupe and sedan as well. Later cars have the closed-loop black pouch-like expansion tank and a different venting arrangement.
I sourced 3 rubber parts from Niemoeller; other suppliers carry the parts as well. Service from Niemoeller was professional and quick.
In addition, I used a silicone based spray as lubricant and got my tubing from a motorcycle shop and my local hardware store. MB sells tubing at multiples of what I paid. The textile frayed a bit at the edges when cutting and this could be fixed with an open flame or some glue/varnish. For an ultra-ultra clean installation, a friend machined some end caps for me out of black anodized aluminium for the fuel lines on my BMW bikes, but I have no spares left.
Parts List:
1 x D 47 101 grommet (111 997 22 81) €7.34, guides 2 tubes through hole between trunk and filler neck
1 x C 47 027 rubber boot breather pipe €14.50, vents expansion tank and hangs below trunk
1 x A 54 225 rubber grommet €1.55, guides vent tube through hole in trunk floor
50cm textile wrapped rubber fuel hose OD 10mm, ID 5mm, €2.00 from motorcycle shop for making various connections
2m plastic vaccum tubing OD 5mm, €3.00 from hardware store
The restoration shop that worked on my car had connected the wrong expansion tank nipple to the venting pipe. The correct connections for the half-moon plastic expansion tank are that the 2 nipples that are together connect to the filler neck, the single nipple vents through the floor. You can see that there is an internal plastic construction that is open at the top and ends at the single nipple. In other words, any spilled gasoline is trapped in the expansion tank while the fumes can exit through the top. I used the rubber tubing to connect the vacuum line to the various nipples. Total time, not including shopping, was under 30 minutes.
I tried all afternoon to post this with photos without success, so here is a drobox link to the pictures:
https://www.dropbox.com/sh/9tuw64ppccfkncp/AACts5SGVZbnHn8kTf_f_Dc3a?dl=0