I think is rather from wear rather than ULSD. Back about 10 years ago, MBs from the 80's were getting fuel leaks all around the same time and having components replaced. Ten years later, it's just time for the early 90's models to go through the same thing.

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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.