fuel leak at injection pump and question re fuel lift pump

On my 75 240d 115 chassis, I have fuel welling up/leaking at the top of the injection pump at the base where the individual line connections meet at the top of the pump- it seems that the 17mm hex nuts on the lines are tight. Does this mean there is a defective seal or something under there?. Also- I'm trying to figure out possible causes of reduced power upon startup and uphill- even though I can easily run 70 mph on the level. I have not yet replaced the fuel tank filter, and the problem occurred before the above mentioned fuel leak started. I'm considering that the fuel lift pump may be weak, and I have low fuel pressure or air getting into the lines. how can I determine if that is the case, and if so is it (the lift pump) easily replaced?. Is the lift pump the thing just under the injection pump that the hand primer pump is attached to, and appears to be mounted to the side of the engine block with two bolts? Thanks for any input