well I did the ball joints and now the right side axle tube in running oil out i thought i was carefull how hard is it to replace that seal ? or do you need special tool to do it?..HELP

 

If your talkin about the 90 then its some work. You may not have damaged the seal but??? pulling the axle out will allow oil to drain out the hole and into the tube where it will sit for a long time causing you to wonder what the hey is going on. If replacement is necessary the front diff cover has to come off and the bearing caps removed and the diff poped out. This is after you pull out both axles again mind you. The seals go in from the inside of the diff housing. easy but time consuming. If you do this it is critical you replace the diff bearing caps the same way they came out,left /right/top /bottom etc. Last one I did the gear came out with some finess, otherwise you will need to squeeze the diff housing at the top and bottom so it relives the gears side load and it can come out.

 

According to some people here the seal may heal itself over time. Make sure your diff fluid is at the proper level, about 3/4" below the bottom of the fill hole. If it's the passenger side seal on a Dana 60, you can change it through the CAD housing hole. The driver's side requires the cage to be removed as apache said. Good luck with it. It's a crappy job. Done it twice.

 

berner is exactly right.
Wait at least 500 miles and see if the leak stops.
It very well could be not a leak at all but rather oil that got by the seal into the axle tube while the axle was out.
Fluid level is very important, more is not better