Hi to all . This beauty has done 70,000 km up to now in 9.5 yrs. No problem except 5 glowplugs during last 3 yrs) untill now. Air is entering the diesel line from the tank. My trustworthy Mercedes garage replaced the tubings (tubes cracked) on the engine. Went to fetch the Benz to day (200 km). Did not want to start at Mercedes workshop. Mechanic suggest remedy by installing Mercedes part called 'nonreturn valve' in the diesel line. According to him it is a modification and is done to all C 250's when tubings are replaced. I am a medical practitioner, so the terminology may not be correct . If this is the correct action, so be it. Please advise.