Rear Driveshaft axle leak - costs to repair
Looking for a bit of advice on an oil leak found whilst having to change a wheel due to a puncture.... noticed that there was a leak in the quattro system that looks to be coming from the gasket between the centre housing and the driveshaft housing for the rear right hand wheel, circled in red in the below photo. The car is a 2005 B7 A4 Avant S Line 3.0TDI Quattro.
Any ideas on what would be needed to repair this - is it usually just a gasket leak or is there likely to be something more serious? Any ideas on how much it'll cost to get repaired?
Thanks for any advice / similar experiences.