bena,
First, you need to go to a an authorized Mercedes Benz dealer and purchase the
correct transmission dipstick and a few of the plastic locking pins for the cap
on the transmission dipstick tube.
Then get your Sprinter up to full operating temperature, and measure the level of
the transmission fluid.
Then add fluid until the level is near the full mark.
If you have no transmission service information, it might be smart just to take your
Sprinter in and have the full transmission service performed.
Roger