Not common as far as I know, to replace the antenna itself, it screws off. To remove the antenna base you have to unscrew a nut, it's under the headliner which is a big pain. The wiring is pretty reliable and is in the base and under the headliner.
Don't know what needs replacing so further details could help.
Assuming the power to the antenna base (amplifier) is turned ON (there's a way to verify this with VCDS/Vag-Com or even through a menu in the radio itself... do a search), the circuitry inside the base is known to corrode... If you look around, you may be able to find a replacement antenna for not all that much money - although as CCBB said, getting to the underside of the base is a pain on the Sedan models...
Be careful with the Chinese ones on eBay... they're not the same quality, although possibly if you stay in town it should pick up most of the stations.
VW TDI forum, Audi, Porsche, and Chevy Cruze Diesel forum
A forum community dedicated to Audi, Volkswagen, Porsche, and all turbo diesel owners and enthusiasts. Come join the discussion about performance, modifications, troubleshooting, TDI, maintenance, and more!