Those two bolts just hold the transmission to the engine via the oil pan. The pan is sealed to the block by the bolts that thread vertically into the bottom of the block. That bolt has nothing to do with your leak. It is likely that your leak is at the cruciform seal which seal the sides of the rear main bearing cap to the block. Pretty crappy design. My understanding is that the rear main seals fail much less frequently than the cruciform seals. Based on the bolt you showed in the picture having what appears to be a threaded insert on it, it looks like the pan has been off the truck before so it might be that there isn't enough rtv on the pan where the cruciform seals end at the bottom of the block.

You also need to keep in mind that this is a British vehicle, and a Rover at that. If it didn't leak then you would be out of oil.

 

That's a fact. Until you are having to add coolant in any instance or like a quart of motor oil or transmission fluid weekly, then you don't have anything to worry about. It's like a cartoon where a water damn has a tiny leak spewing...the guy sticks a piece of gum there and it stops, he smiles, wipes his hands. A moment later 2 bigger leaks start spewing from elsewhere.