91 300E ATF leak from torque converter seal?

Thanks again for all the help I have received here. A few more questions please. I notice while changing my oil that what I believe is the torque converter (the big round thing between engine and transmission) is all wet. The car has 110k miles and no visible leak on ground. This is probably a simple question but does the torque conv. and Automatic transmission use the same ATF source? Where is it filled from in the engine compartment and should I check the level to see if it is low? Must the seal be replaced, the car runs fine otherwise, what damage would I do? Can I just keep on making sure that the ATF level is correct? What would be the procedure to change the ATF fluid and filter? Thanks