Transmission leaking
 

I noticed that at the bottom of the transmission there is a bit of ATF accumulating.
It is right where the gearbox and engine join.

There are no oil stains under the car. It idles for about 5-7mins in the garage before I take off and still no oil stains.

The leakage is very minimal, and it seems that it is only while running.
What could this be? And is it an expensive fix?

Also, the ATF is red in color. Is this the correct color of genuine Mercedes ATF?

"Yes" that's the right color and it is most likely the front pump seal that is leaking.

Is it a difficult or expensive fix?
One mechanic (which I am going to stop going to him) told me only to fix it once the whole gearbox will come out for other maintenance, as he said even though the miles are low, the age is high and hence there are rubber bits which will harden etc

seal is not expensive BUT the box has to be taken out for installing the seal,in itself a simple replacement .
mak