Do you know if it is a DIY job to check the auto fluid level ?

Wouldn't like to say, if its the 7 speed (it probably is being a 320) then i believe replacing the fluid is a very specialist job whilst linked to STAR system, i would think the days of a good old transmission dipstick were well and truly over by 07 at MB.

These are not really DIY vehicles, though assuming the car in question is a facelift at least the ridicilous SBC braking system had been dropped by then, meaning DIYing brakes you are more likely to retain your fingertips than with an SBC pump suddenly waking up at the wrong moment, ouch.

If you have a new wave vehicle go to youtube and put your problem on there there is a lot of good videos on how to , i drive a Renault auto that has a level tube up inside of the drain plug to drain it then put it back in plus the plug to fill up with fresh ,then get the engine up to temp undo the drain plug [rubber gloves] and with the engine running in neutral [ front wheels off the deck ] undo plug if fluid starts to run out at a tricke thats the level well thats on mine anyway ,any automatic if overfilled will come to greif be sure you know what your doing iv done mine and it works a lot better than when i first got it ,

Iv seen some automatics and they have to have the pan taken off just to change the fluid because they dont even have a drain plug

Some units are classed as sealed and you need a special pump so check it out thoughly before you attempt to do anything !