A typical problem found on Defenders, Ranges and Discoveries is shimmy teering.
In some cases it's due to play in the stabilizer bar which runs from the chassis to the axle. It's mission is to position the axle firmly.
On both end of this bar sits a rubber insert. Those wear out and in turn give room to the bolt (red arrow in upper picture) to move. As the bolt is harder than the axle metal it sits in it wears the holes. This can only be detected by exact examination with the bar off.
The bolt on the right is from our Discovery. The red hand points to the outer (toward front) side. Here you see just a little discoloration where the bolt moved. This hole was almost good.
The back side however had badly worn treads (between green hands). The bolt rubbed in the hole, enlarging it considerably. If there had been no treads I bet it had worn much less.
A bolt like this must be discarded as you will not be able to tighten it p correctly. Luckily it's nothing special, just a plain M14 bolt, rated at 8.8. Use also new self-locking nuts.
The rubber inserts present no particular problem but you will most likely need a press. Mine showed only 0.5 tons when pressing out and in. Coat the new metal sleeves of the inserts with copper grease. Do the same on the new bolts.
You MUST check the bolt holes when the bar is off. The problem is that a new insert will be tight for a short time as it sits on the metal of the sleeve. If the hole is enlarged it will start moving again after a few days.
Curing enlarged holes is easy: Just weld a thick washer over the outside where it's worn. Don't use stainless bolts or washers in this application.
I found this happening on a 90 and on the Discovery.