If its pulling to the right id say its the right side caliper. X2 on the panhard bushings have some one push and pull on the bumper while you look at the bushings.

 

Sometimes these Disco's will leak oil out of the steering return hose or another place and as you drive, the drips can be drawn to the L. wheel, often coating the caliper and some getting on the rotor. I have had this happen. It's worth checking to see if your L. front inner wheel/tire is oily and if so, try to resolve any leaks.

 

Left, if it is pulling to the right.

 

fwiw.....I had the death wobble bad when I first got my truck, long story short...it was the panhard rod ....not the bushings, but the bolts were just loose enogh to cause the shake. I noticed it one day when I was changing the oil and used the rod as a grab point to pull myself under the truck !

 

Small update. Tried to take the right caliper off and stripped the fitting on the small metal line. After a few choice words, I tightened everything back up and tried to source a replacement line. A few Rover sites had it for 60+$!! Nuts! I managed to find a Raybestos part number (working in the industry has its perks) and found it on Rockauto for 7$, I opted for the 2 day shipping so it should be here Monday. Still can't believe the price difference.

 

Why fool with the right one? You said it pulls to the right under braking, not driving. That would indicate to me that the right one was working, and the left one was frozen (open) and is providing no braking force. If it was pulling to the right while you were driving, the I would suspect the right one was dragging, and thus frozen.