lately its been taking a long time for my car to start. i almost always have to crank it for about 2 seconds, even if its still warm, but every once in a while it starts right up. the car runs fine after a few minutes, but occasionally there is alot of smoke when i start it in the morning (gray smoke). i just had the oil changed and it is still doing this. my glow plugs seem to be operating normally. could this be a compression problem? bad fuel? something else? it wasnt doing this 6 months ago. it seemed to start when i changed to Mobil1 0w-40, but ive changed it back since then to 5w-40.

thanks

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1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350