When you checked the tranny fluid, did you check it hot or cold?
It should be checked at operating temp (hot) at idle and should be right at the upper mark. If you checked it cold and not running, then the fluid level should be below the lower mark. At that point I think it will read about 10mm below the lower mark if filled properly.
And yes, a fluid and filter change sound like a good idea.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.