Straight from the FSM for a transmission fluid level check:
CHECKIN FLUID LEVEL
1. Be sure transmission flyuid is at normal operating temperature. Normal operating temperature is reached after approximately 15 miles (25km) of opreation.
2. Position vehicle on level surface. This is important for an accurate level check.
3. Shift transmission through all gear ranges and back to Park.
4. Apply parking brakes
5. Verify that transmission is in Park.
6. Wipe off dipstick handle to prevent dirt from entering fill tube. Then rempve dipstick and check fluid level and condition.
7. Correct fluid level is to FULL mark on diostick when fluid is at normal operating temperature.
8. If fluid level is low, top off level with Mopar DexronIIE/Mercon. Mopar Mercon II can be used but only if Mercon is not available. Do not overfill transmission. Add only enough fluid to bring level to Full mark.
9. If too much fluid was added, excess amount can be removed with suction gun and appropriate diameter plastic tubing. Tubing only has to be long enough to extend into oil pan.
CHECKING FLUID CONDITION
Inspect the appearance of the fluid during the fluid level check. Fluid color should range from dark red to pink and be free of foreign material or particles. If the fluid is dark brown or black in color ans smells burnt, the fluid has been overheated and must be changed.
So, there you go. The biggies are to have the temp up to normal, set the Heep on a level surface and run it through all of the gears just prior to checking the level. Running the gears ensures that all of the passages and solenoids are filled... And, be sure it is in PARK not NEUTRAL.
I would be very concerned about the overall condition of the transmission. Pull a sample of the fluid prior to the next add and look at it under magnification. In particular, look for metal. Some friction material in the pan is considered normal as the friction plates wear and that material has to go somewhere.
You should never find metal in any fluid in the Heep...
What I always found interesting on my Mercedes was that all of the level checks had a specific temperature (in degrees C, of course). Not only the transmission, but the engine also. None of the check specs were tagged as "normal operating"... Then again, the pan on my 280SEL 4.5 (gas V8) held 8 quarts, so there was a large differential between cold and normal levels. Oil changes took slightly better than 9 quarts as the engine oil cooler and it's lines had to be drained and refilled prior to engine start. 1 Litre capacity on the cooler system...
