I did a little investigation in ISPPI and for some reason, the return rubber hose is greyed out on the diagram. On the older W124 300D, the return rubber hose is there and the E300D 124.131 is not listed as an applicable vehicle. It seems to suggest the E300D doesn't have a rubber return hose, but you claim to see it. Nevertheless, the part number for the older W124 with the rubber return hose is 124-476-03-26. Pictures of your tank would help.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.