240D Fuel leak and rear differential leak
 

So my rear differential is leaking oil. I have never messed with the rear diff. It seems to be leaking on the side where the drive shaft attaches. Is this an easy thing to fix. Also i punctured a fuel line coming from the tank when i was sandblasting the control arm in the rear. There are 3 lines together and they are all really rusty. How hard are they to replace, and also is there a shut off on the tank somewhere so the fuel stops leaking.

fuel tank , line leak
 

there is no cut off you have one main fuel line with a fuel strainer in the tank if that line is leaking you need to siphon all fuel out and get a new line you can stop the fuel leak with a pair of vise grips crimp the hose to stop the fuel from leaking, you have three lines one is a vent one is a return and the odd one by itself is the main fuel line, all these metal lines can be made up with new line 5/16 will work you can use pex also very cheap and works great will not rust just use hose and clamps to connect it where it needs to go. 5/16 pex......

how about the differential. Is the seal called a differential output seal?

rear differential seal
 

it sounds like your side cover seal is leaking on your differential, axle has to be removed to repair this.

leaking differential
 

just go ahead and pull both axles and install new side cover axle seals,