I had my car up on a friend's lift a couple days ago just to have the opportunity of seeing the condition of the underside of the car and noticed a leak at the right side differential pinion seal. Is this something that can be done DIY or is it best that I take the car to a mechanic for this? I have never before had to work on a differential.

 

That's the output shaft not pinion. Not a separate seal, just a sealed bearing. Not too difficult to change out but won't be quick or cheap.
You will need the bearing and retaining collar and access to a press.
It is possible the leak may be from oil leaking past the bearing due to failed bearing/bore O ring rather than actual seal but you won't know till it's out.

 

CHECK THE DIFF BREATHER!!!!!!!
Too much pressure in the case will cause leaks!

 

Alright, so I should check the breather, unclog it, add oil, and drive a around, then inspect if the leak persists?

 

I once replaced the 'O'ring seal in an 'in-line' diff (X100 or X308) that was in factory warranty.
The seep was not bad so I thought I had it fixed with the new seal. A few weeks later the car came back with the other stub axle seal seeping.
I pulled the bearing/axle out and it 'SUCKED BACK IN'.
I pulled really hard and it came out with a sucking-POP noise.

Vacuum I thought!!!!!!
Unscrewed/removed the breather assy on the top of the diff and it was blocked solid. (the little rubber valve was stuck.
I ordered a NEW breather assy and installed it. NO MORE LEAK!!!!!!!!!!!!!!!

Whenever I see a stub axle or pinion leaking, the FIRST thing I do is check the breather. (once bitten.......)

 

chances are the breather is gonna be good. use a ratcheting box end and it’s out in 2 seconds

if it still leaks do not touch or attempt to fix just buy more oil

 

I removed the breather today. It had some gunk on the outside, but the inside looked cleanish. I soaked it in a degreaser for about 2 hours and cleaned it up. I confirmed it wasn't clogged and installed it on the diff again. I then cleaned the area of the leak. I will give it a week of driving before I check again to see if the leak persists.

 

Puerta Rico,

I've determined that what my XKR needs is a "Good Dentist"!

Billy Clyde @ Cinco Ranch