could be a pressure problem?
you can change the diff part of the oil..any SP3 will do..just look at the diff,you will see 2 drain plugs and 2 fill plugs,the ayc fill is way up on the back of the diff..24mm iirc and there is an "ayc oil" stamp on the diff housing and the drain is cl0se to that too.
a specialist will change and bleed the pump part of the diff , or you can bleed it yourself
(need 2 mates tho and 4 jackstands) or blled it using evoscan..dunno if it works for a 4 with evoscan?
best to flash out the fault code for the ayc and go from there.