Many MB fuel filters each year for tech sessions.

I have seen an increase of petro sludge/goo, and have been tempted to send some samples for lab analysis.

Most I attribute to alternative fuel, some seems to be from ULSD breaking down rubber hoses/seals + very slowly breaking down old tank sludge.

Hose and O-ring replacement has gone up 50% this past year, suspected cause is ULSD.