To my knowledge, the rubber orings used by MB are a Buna material.

Your engine uses some orings at the ends of plastic fuel lines leading to and from the fuel filter and IP. Suggest you look at those next to resolve your hard starts. Sounds like you have a minor leak allowing air to enter somewhere. You do not have a manual primer pump. Priming is accomplished by cranking the starter manually (using key, rather than auto start feature) for 30 seconds. Repeat 2 or 3 times until it catches. After 3 tries let starter rest and cool off for 10-15 minutes.

Unless an oring was pinched when the delivery valve seals were replaced I could not imagine they would deterioate to the point of leaking in one month regardless of the fuel type used. Deterioation usually occurs when the fuel type is changed and the aromatics used in the different blends (LSD vs ULSD for example) cause rubber componets to fry out and shrink.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)