Here is a picture of what my differential has been looking like for a couple years now, and i'm a complete noob...so can anyone tell me what should i be worried about, or what do i need to fix so there will be no more oil on the outside...and what part might i have damaged over the years. By the way its a 99 dodge ram 156,xxx miles

http://i34.photobucket.com/albums/d1...fferential.jpg

 

have you ever changed the fluid? You should take off the pumpkin and put sum new fluid in and remember to use rtv selent for a gasket.

 

R&R the diff cover clean the mating surfaces put some rtv on the cover, fill it, and put alittle on the fill plug....just in case. hopefully you have changed the fluid before in 156,xxx miles or else maybe you might have problems later

 

My truck has 250,xxx I have no idea if the previous owner ever changed the diff fluid, would it be safer for me to just leave it alone or change the fluid?

 

you should service the differential(s). its real easy.
if you have a limited slip (as opposed to open) you will need the friction adder.
http://www.pavementsucks.com/tech/diff.php
your leak looks like its coming from the rubber plug. there is a vent tube at the top of the axle, make sure its not stopped up and building pressure.