these are sealed transmissions... they don't want customers fiddling with the amount of fluid in them. Apparently from what I have read and heard from other people is that this transmission is VERY sensitive to the amount of fluid that is in it, and that something like 1-2% difference can through it off. If you already didn't know the trans on LX's are a Mercedes design and are quite strong (albeit it seems they are programmed to not be as agressive as people would like). Anyway getting back to your question you don't need to check it or change it, the fluid in these are good for I THINK 100,000 miles.
But there has been a little problem with these tranny's in the LX platform, in the magnum and 300, the AC condenser sits right above the fill point that you just mentioned and drips water on it. Some of this water can infiltrate and cause some problems, and it doesn't take very much either. I don't know if this is a problem on the charger... I haven't heard anyone at all really complain about it. So i wouldn't fiddle with it.
I bet you weren't expecting this long of an answer
btw welcome to this place... there are some awesome people here