Have you had your gears changed? If it is a leak from the seal, just pull the cover, and reseal it. Be sure to check for any premature gear wear, clean out all of the old fluid, reseal, refill, and be on your merry way. Should be an easy job to do. Just remember to use some high temp silicone. Lastly, I don't think the differential fluid should be red unless you are using redline or some other synthetic. Red is typically a tranny fluid color.