Long Crank but no Start

[probro529]

So some background info I bought this new to me w201 190D 2.2L last year in august, and its a phenomenal car. I love it.

But the car has had some issues when I bought. It didnt start at all at first and once I dropped it off at my mechanic (who works on older euro spec cars) he said the timing was off and got it running good as new. The car survived the harsh canadian winter of 2015/2016 as well as this passed summer.

Apart from small jobs of changing the serpentine belt and tensioner and the car is my dream car. But in the recent weeks the car developed a 'no cranking' problem. To specify, one day I went to go for a cruise and it didnt start on the first attempt, no use for glow plugs as it was 20+C outside. After a second attempt of cranking it fired up and ran fine. I figured the problem went away until about 3 weeks ago.

The car has developed a no start issue. When I say no start I mean I have to crank the engine about 5 x 15(seconds) in order for it to catch and run. Once it runs its runs great. But whether its a colder or warmer night its the same problem. My dad and me believe that the diesel fuel is not maintaining pressure and returns to the tank or receeds from the injectors.

I already went and fried my starter after a long attempt of cranking and white smoke, suddenly my starter smelled burnt and was smoking hot. I got it inspected and yes, the gears were ground into a metal powder, so I got a new one installed. The new starter is well newer but the "fuel receeding" problem is there, if that can be it.

My glow plugs are fine, filters are all new, done within the last few months. I cannot figure out the issue. Perhaps a cracked or loose fuel line? But I spent all day checking the lines and crawling under my car with no sign of wet diesel spots on engine components or the driveway. Like I said after 4 or 5 attempts of 10s - 15s of cranking the engine sputters, attempts to'catch on/fire' but fails. When all hope is gone to leave/tow it, it will catch on, fire and run like there was never a problem.

Also as a quick P.S. when the car is turned off for more than an appx 5hrs the troublesome cranking has to be performed. But if the car was off for only a couple hours and is semi warm like 1-4 hours, it will start up with no problem.

Any thoughts or suggestions would be great. The entire MB community is fantastic and I would hate to see myself part with a beauty like this. I am a student and will make my best attempt at giving prompt replies. Thanks everyone

P.S.S - I can record a video to show its rough start if possible.