Potential ATF leak

[VenomX]

The other day I saw a rainbow like mark on the ground infront of my car after it had rained, thought nothing of it.

Just today I looked under the car, and the sump which holds ATF appears to feel very greasy and have a lot of dark brown substance on it,



Is the best thing to do get a dispstick and check the levels ? If they are low I will take it to a mechanic as I am not willing to do work on it myself due to clearance issues.
Car is a 2002 W203 C240 with 34K miles on the clock.

The photo of the rainbow mark was from last week. The photo of the stained tissue is from today

 

[M80]

It isn't uncommon for the pilot bush 'o' rings to weep.
That's the electrical plug on the o/s fore of the gearbox.
During an ATF change it's considered a service item.

 

[VenomX]

I will try to replace the TCU plug myself, is it as straightforward as YouTube videos show ?
This here...