Yes it can be marginal fuel but unlikely. A couple of thoughs come to mind. If it has a block heater hook it up for several hours then try. Second is to give a little starting assist by spraying a little starting aid into the intake with the air cleaner cover off. But you have to be very careful. Read some posts under either or starting fluids first. If the block heater is not possible just leave the car till ambient temperatures pick up a little. To fill in the time again read some posts on the glow plug circuit as car may have stopped being used because it had one or two bad glow plugs. Most indirect injection engines really like all the glow plugs to be functioning or they will torment you. Welcome to the site and if are short on space with too many people giving you free diesel mercedes cars I am willing to help you out. No sacrifice is too great for a new member.