gen4 - oil dripping from kingpin

Now we know it has been in an accident severe enough to bend the hub, I'd say it is only the axle oil seal that is leaking and the bearings are probably ok.

This may be because the axle tube is bent pulling the halfshaft to one side- as Martin says check it for straightness or it might be that while the hub was bent the halfshaft wobbled about and wore the seal out.

Find out what it is first, if the axle tube is bent it can be straightened (or replaced), but you will have to take it off to do a proper job.
In The Olden Days LandRover did a tool for bending their axle tubes in situ, but this was for correcting steering geometry, and I've never seen one in real life, only in a Series II workshop manual.

 

The inner seal to the diff was the culprit. The axle is fine, looks suspiciously like new. We suspect the previous owner replaced it after the accident. I can't understand why they didn't replace the €4 seal too... We also changed the outer knuckle seals, overall €25 for parts. Hopefully we won't be leaking anymore


 

I'm feeling the optimism however a long time ago my dad was driving dreadnought when some born again biker decided to slide a 750 under the sill and then back axle. Didn't noticeably touch the front axle but it did very nearly put it on it's roof. The insurance did finally get the repair right after far too much noise but unbeknownst to everyone the force of nearly tipping it over and the subsequent landing did a number on the kingpin bearing seats on both sides enough that it failed it's first mot at 3 years old and every year after that I had to replace them until eventually it became apparent that the seats were oval and wouldn't hold the bearings which allowed them to move and make everything worse. My point here is just because the axle looks good doesn't mean it actually is and not fully knowing how violent the collision with your car was leaves room for problems to hide.

To elaborate, this is why I think the axle was replaced. It looks like the tunnel was severely bent, then repaired, probably by cutting and welding... I doubt the axle survived that. The kingpins are fine, we've checked them and they provide the necessary resistance to avoid death wobble and indeed, the car runs straight under acceleration and braking without pulling or wobbling with speeds up to 140km/h.



P.S. 24 hours later, there are still no leaks, so that's solved I guess.

Well something new popped after this intervention...

I noticed that whenever I switch to 4H at speed, a new sound is being heard from the front, something like a constant "brrr", sorry for the lack of better words to describe it. Sounds like a resonance or an excessive play between gears. It's immediately heard after I pull the lever, so it doesn't seem related to whether the hubs are locked or not. It's most easily heard in 5th gear with speeds about 60kmh or 40mph and with maintenance throttle. The sound is not so strong when accelerating or decelerating, but it was definitely not there before this procedure. Previously there was absolutely no sound change when switching between 2H and 4H.

After the seal replacement, my mechanic also drained the differential oil and filled it with 80W90 oil bought from the Suzuki dealer. I wasn't present there, but he told me that there are lots of metal shavings in the oil and that he suspects that the diff needs replacing. His suspicion is that the previous owner put thicker oil to cover up the issue before selling. 
Is it possible that my mechanic did not put back the axle correctly? Are metal shavings (not shards) normal in the diff oil? I'm not thrilled by the idea of replacing a whole diff...

Sorry but metal in oil is never good. There are degrees of bad but it's a scale of bad to catastrophic. It's going to need opening and inspecting.