Hi Felix. The transmission fluid is very dark because this truck works over 16 hours a day fully loaded at very low speed, and you believe or not that oil it's just 5 months old ...
It pumps the fuel back into fuel filter, once the filter is full need to keep pumping till the air on pipes for the common rail gets out through the fuel return pipe on the tank . After opening any fuel line you must pump the whole air out from the fuel lines otherwise the engine will have a long delay start. because the injectors are not capable to expel the air out from the rail there's also high risk to ruin the fuel pump from running without diesel
Yeas, it can be changed. I would make double sure the leak source is not fron some gasket or seal. Clean, leave the engine running till the leak source can be confirmed. Remember, when ordering parts, ask also for any seals and gaskets kits for all the parts to remove.
