I have a 2003 Ford Explorer, 4wd, 4.6 cu in, 5 spd auto. I'm looking to replace the rear differential oil. The Owner's manual specifies 75W-140 synthetic, however the differential case casting has 75W90 cast into it. The tag bolted to the differential has a series of numbers and an L, so I'm assuming it's a limited slip. Any suggestions as to which oil is correct?

 

Usually if you follow the owner's manual you will be OK.
You can purchase the additive and add it for limited slip.
If you provide the vin to a Ford dealer parts dept , they should be able to tell you what is in the vehicle and have the additive if you need it.