2015 XF S Rear diff noise/leaking pinion seal replaced 2018

My 2015 X250 XF 3.0D S had an advisory for a rear differential fluid leak on its first MoT in 2018 at 15,000 miles. A new seal was fitted by the Jaguar dealer in 2018 and I assumed the problem was fully resolved. However, I took the car in for a Jaguar dealer service today at 40,000 miles and was told there is a noise coming from the differential and that rear diff pinion seal is moist. The noise is very slight and I can only hear it from the passenger seat, it just sounds like the air conditioning fan is on at a very low setting speed. The car still drives 100% fine. When my wife turned off the engine yesterday, I noticed a short noise from the rear wheel on the over run.

I’ve read lots of horror stories online about XF rear diffs failing and it costing a fortune to replace them. Can someone recommend the best course of action to take?

I’ve found a transmission/differential specialist not too far away and I was thinking they should be able change the diff oil and put a new seal on. However, if the diff is already making a noise is it already damaged to an extent that a diff oil change won’t improve things?

Also, I’ve heard that changing the diff oil and seal involves rebalancing the diff and this is a tricky job and that the diff won’t be as smooth afterwards. Am I best to take it to a transmission/diff specialist rather than the Jaguar main dealer? I can’t imagine the Jaguar dealer has that much experience of changing diffs unlike the specialists that work on transmissions and diffs every day and the Jaguar dealer wants £132 just to look at the problem again!

Am I best to get the diff oil and seal changed at a specialist and hope that the noise is resolved by this. Which is the best type of diff oil to use and am I correct in saying 0.85 litres should be used?

In the very worst case scenario, if the diff fails in the future, I have seen a few second hand diffs on eBay for around £250 - how much would it cost to get a used diff fitted and is it possible to fit a used diff without losing the smoothness of power delivery associated with the XF? I’ve read online that it can cost several thousand pounds to replace the diff but as I say there are always quite a few used diffs on eBay and I can’t imagine that the labour would be thousands of pounds at an independent garage.

Ideally, I’d like to keep this car for many years to come - aside from this diff issue, everything is 100% fine with it but I am worried that this rear diff issue will be a persistent pain

I don’t know much about the intricacies of issues related to the differentials on these cars. Still, I wouldn’t hesitate to take it to a specialist to get their opinion and possibly have they try to mitigate the damage. As you say, they do it every day and are probably vastly more qualified to do the work than the average Jag tech.

If you do end up replacing it at some point, it shouldn’t be insanely expensive if you go with a used unit. I don’t recall anything out of the ordinary when under mine that would make swapping it out of the ordinary in terms of difficulty. The swap should be pretty straightforward.

Thanks Brett, much appreciated. I was pretty worried initially but it doesn’t sound as though swapping over a used diff will be that much of a problem. I’ll definitely take it to a diff specialist, they should be used to dealing with this type of work and main dealers are insanely expensive even on relatively small jobs