I would first adjust the valves and perform a compression test if necessary. Also, Check out the following link to see if you have the same kind of fuel problem as stated in the post:
300SD Hard start after not used for a few days
Low compression (caused by worn out rings or tight valve clearnance) will give a cold starting problem. If you have a fuel problem as in the link above, you will not smell diesel or see smoke from the tail pipe during cranking.