The part number depends on the make of fan currently fitted, you can't mix and match. Siemens and Temic are the two makes given in the parts cat.
Fan on AXX engine
1K0 959 455 ET -Siemens (200W/295mm Right).
1K0 959 455 CR -Temic.
1K0 959 455 Dt is 300W/360mm left Siemens
1K0 959 455 CQ is 300W/360mm left Temic
1K0 121 207 BB 9B9 is the actual Cowl.
All the above is not cheap, comes to around £360, 60 for the shroud and 160/140 for the fans.