How do you get Transmission Fluid in your 1991 Mercedes 300E It has a special Cap On fill tube?

i would like to know what kind of Transmission Fluid i use.

-

-

Added:

If the tranny was dealer serviced their may be a locking clip on the cap. This is a one time use break-away item that the dealer uses to deep people out. If it was installed you would have to pull down on the tab to break it loose and discard. Then release the cap by release a clip that is secured to the dip stick tube.

You can use DEXIII/Merc fluid.

Hope this helps.