Tranny/rear whining and grinding...help!

So I left school this morning in Georgia to bring my buddy home in Maryland, then head home tomorrow to NJ. I get about 200 miles or so, and after that time I noticed a slight whining coming from under the car on deceleration...not necessarily on the brakes, just coasting even. As I got farther it got worse, but the car was driving just fine. So I get to Virginia about 40 miles from my buddy's house, and I am coasting down a hill and not only is it whining, but theres a slight grinding/clanking sound coming from under the car...what I thought was the tranny...but wait it gets better. So I pull into a gas station, call AAA and have it towed the remaining 25 miles to my buddy's house. As we are taking it off the flatbed, there is a puddle of rear end fluid on the flatbed and it's clearly leaking from the differential. At this point I don't know what the problem is! I thought it was CLEARLY from the tranny cause I could feel it in the shifter, but I guess I was wrong. I stopped before it got too bad, and had it towed and my dad is coming down to Maryland with the trailer tomorrow. What could this be? At first I thought it would be either the clutch cable going, or the throwout bearing, but I replaced the throwout bearing, new clutch, and rebuilt transmission 2 years ago, and maybe only 8k miles it! Help me please!
 
Thanks guys. I called the guy that has done many race transmissions for my dad and did my rear end rebuild/gear install, and after I told him the symptoms he said it was a classic case of the crush collar on the pinion gear going bad. This seemed weird to him considering he just did the job on my car about 4k miles ago, and this should have lasted WAY longer than that. Were gonna take the car to him next week and he said he's gonna make good on his work, because there is no reason it should have given out after such a short time.
 
I doubt the crush collar failed.:nono: The pinion seal probaly started leaking lost to much fluid and the bearings started to wear faster then normal due to lack of fluid. bearings wear = more movement = grinding

but I may be wrong:shrug: I think its time for me to :Zip2:
 
I doubt the crush collar failed.:nono: The pinion seal probaly started leaking lost to much fluid and the bearings started to wear faster then normal due to lack of fluid. bearings wear = more movement = grinding

but I may be wrong:shrug: I think its time for me to :Zip2:
Yea, this makes more sense because it got worse as the drive went on. I probably lost all the fluid by the time it started grinding.