can I only fill from the bottom? Is there a fitting to to bottom of the Trans pan that I need?

 

Yes, you fill and drain from the bottom. There is an excellent fluid change DYI for the 722.9 on this site (including part numbers. Verify #s with your VIN). Search for it. You will need special tools to carry out this service - not expensive at all. Get ATF134 fluid. Make sure you have a torque wrench. Do not over tighten the pan bolts (you must replace them - they are torque to yield).

Note: The AMG's (slk55) DO NOT have a torque converter drain plug. Make sure you measure the fluid you drained and add that back with 1 liter more. If you let it drain overnight or several days, you'll get about 0.5l more out. Overall, you should drain about 5-6 liters.

It reads a lot harder than it is.