Okay so I think my axle housing is Warped on my 97 Toyota 4Runner the axle seal that is in the passenger side is leaking gear oil all over my rear brake can't get the seal to seal in right so my question is how difficult would it be to take the yolk out and put it in a different axle housing unit I haven't decided to do this because I don't know much about rear ends any help would be greatly appreciated on the subject

 

Leaking rear axles is, unfortunately, a somewhat common occurrence on a higher mile and (by now) older 3rd gen.

Some common causes - just to rule out before you go hog wild with a complete axle swap:
1) stuck breather - as the gears heat up and cool down, the air in the axle expands and contracts. And air has to go in and out. On top of the differential housing, slightly to the driver's side, Toyota uses a fitting with a 'wiggly' cap on it. In theory, it let's air out easily, but only slowly allows air back in, trying to limit how much water gets sucked in if you go through a deep puddle, for example. These get stuck - dust and crud sticks the wiggly cap in place. Then, pressure builds up in the axle housing and finds a release through the seals. Fixing the breather will often stop the leak, but you still have to clean up the mess inside the brake drums. It's best practice to replace the brake shoes - you can't really get that oil out of the linings.
2) worn seal - they do wear out. 200 - 250k? After you've made sure the breather isn't stuck, go ahead and swap the seals themselves.
3) replaced axle bearings and incorrectly located seal ring - for some damned reason, Toyota has several items pressed onto the axle shaft. The bearing, the ABS sensor wheel, and a sleeve that the oil seal touches. And, contrary to pretty much any other stack of pressed on items, these are *NOT* all pressed on touching each other. There needs to be some air gaps between some of them. If they are all pressed on together (as some machine shops will do, out of habit) then the seal sleeve will be too far outboard, and will not touch the seal itself when assembled. So if you've had the bearing replaced and are having troubles with it - look at that.

Other than that, a rear axle swap isn't all that hard. It's easier than messing with the front axle. There are 5 control arms, parking brake cables, hydraulic brake lines,ABS sensors and wires. And locker wiring if you have a locker. You have to be able to securely hold the vehicle up while the axle is removed, and it can take some grunt to wrestle the new axle into position and get all the control arms to align. But it's all pretty straightforward, nothing alignment related (like the front end).