I own a 2018 Octavia vRS 4x4 Tdi, currently on 20200 miles and I decided to have the Haldex serviced (gauze clean and oil change) and good god am I glad I did. 

 

As you can see from the pictures the gauze (which on the gen5 is the only accessible/ changeable filter) is completely caked in gunk and to be honest will most definitely been having a negative effect on the 4x4 system. 

 

I strongly recommend you service yours at least at 20k intervals - certainly for the gen5, can’t speak for others!

 

Got mine done at Darkside Developments along with a remap but I’m sure most VAG specialists can do it. 

 

 

That’s pretty bad for the miles the car has done. Darkside definitely know what they’re doing.