Had my disco since December and haven’t used the diff lock yet , and I’m glad. First time changing the lube and this is what I find on the bottom magnet. BIG CHUNKS of gear.

So... Any guesses as to why this happened? what ought I do if I want to use Low gear in the future?

 

First, the diffs are put together, or should have been, with precision. Therefore, there should be no movement outside of normal movement. If something comes loose inside from normal wear and tear, then these bits can get caught in the cgs and start all kinds of problems as they wear down more and more parts. It could be that your bearings are wearing down (the most likely first culprit). You'll want to drain the entire differential and look inside. If it's your bearings, just replace them (along with the seals). But, if the cogs inside have started to get chunked up from this metal, you're in for some repairs. My best guess is the softest metal inside the differentials is going to be the bearings and they wear out the fastest. Check those. Drain the diff. Jack up the Disco. Take off the wheels. Pull out the axles. Yank our the bearings. Inspect for wear and tear. These should be replaced with some frequency (Check manual for exact mileage). And, your diff should be changed every 30k.