Hello:
I need to know where to add transmission fluid to a 1984 500SEC mercedes. I believe it may go in the same place as the dipstick to check the transmission fluid (red cap), but I need to be sure. Also, how much fluid should the vehicle have? I see there are 2 lines on the dipstick, should it be filled to the uppermost line? I rally need this information urgently, as I need to drive the vehicle tomorrow, and when I checked the fluid, it is VERY low.
Thanks!

Yes, you can add fluid through the dipstick tube (Red handle)
Use DEXRON - II
With engine at operating temperature, shift transmission through all gears. Check fluid level in PARK, and add fluid as needed. Just a little at first to how quickly it moves up the dipstick.
Ideally, the correct level is anywhere between the two lines. Those lines mark the acceptable upper and lower limits for that transmission to operate properly.

Usually the top mark is where the fluid "should" be. The difference between the top line and bottom line is 1 pint.