Oil leak D1 300tdi

Hi all I seem to have an oil leak from the rear of the engine suspect crank shaft oil seal been dripping a bit but now seemes to be getting worse I put one of those oil additives in that supposed to seal leaks I think it stopped a bit but but not all. The question is what to do to replace it, engine out or gear box out its an auto by the way.
My other question is how do you fix a roof rack or roof bars to a P38 Range Rover.
Many thanks.