Leaking from end of axle

On the drivers side rear there is a dark fluid leaking out from the end of the axle, where the caliper mounts. I first noticed it right after I had my 4.10's installed by a local shop that installs gears in a lot Mustangs. I was driving the car home and I heard a noise that sounded like I ran over a full soda can. So I just assumed the the wetness inside the tire was just that. The car still drives fine and I assumed that everything was good. That was 4 weeks ago. About 1 week ago I went to do a burnout and it peg-legged, the wheel not spinning was the one where the leak is. Yesterday I noticed that there was more fluid in the wheel and there were drips. I checked the brake fluid hoping that that was what it is but it is still where it always has been. I assume that if the brake fluid has been leaking for a month that the reservoir would be lower. So what could it be? Could the shop of broken a seal or could it be the hub? I'm worried as this is my DD and I can't afford to be replacing these parts. Thanks,


Preston

Is there a way that it could have been the shops fault? How often do they blow in these cars?

Preston

Well, I researched where I wanted to get the gears installed for a long time and this shop came with a great reputation with the local car guys, both GM and Ford. They post on the local car forum and are very helpful. I have a message out to them now because there is also a slight whine at 45mph with the gears. So I gues we'll see.

Preston

They are motive that I bought from Brenspeed on eBay.

Preston