Thanks. A well known e-seller has failed on my delivery so it will be a few days before I can progress this. Optimistic the oil in there is OK having been changed twice and will be OK for a long round trip.

Prior to my trip last weekend I decided to change the oil again so nipped to Halfords. The oil that came out was improved, but still not quite right. However following a 400+ mile round trip I've changed it again and it looks almost normal.

Anyway, I think I'll just monitor it for a while and see what it looks like when I draw a bit out every month or so. Thanks for everyone's comments and advice.

When people check or change the diff or PTU oil, do you always change the plug washer?
If so, is there a source to buy these in bulk, I notice that you can buy copper washer sets from Amazon/Halfords etc but I don't know if any of these are the correct size.

I reuse mine until well knackered.

Doesn't take much to file a copper washer, if slightly too small.

Flatten surface on wed n dry and then anneal with a blow torch . Jules

Use a Dowty washer, which is designed to seal against high pressure oil line fittings. They are available in a multitude of sizes.  Hyundai Ioniq 5 Ultimate. The family car.
2009 Rimini Red SE TD4. Gone.
2006 Tonga Green i6 HSE. Gone.
Audi A5 convertible, my daily driver.
1972 Hillman Avenger GT, the project.

Serviced the Haldex again today (2nd time in 2 years ownership and 20K miles) and while I was there checked the Diff oil again. It is still clean as a whistle. I've no idea what caused the original problem but suspect either I managed to contaminate it when I changed it, or the wrong stuff was in there previously. Anyway happy its ok now.

thanks for the update - always nice to know when something goes right Jules