This tutorial is for an Mk2 Octavia but i would imagine the process is similar in the golf.
Also usual disclaimer
NEITHER I NOR MK5GOLFGTI WILL BE HELD RESPONSIBLE IF YOU ATTEMPT THIS YOURSELF. YOU DO SO AT YOUR OWN RISK!!Ok here is the OEM shark fin Antenna - Part no. 1K0 035 507 J
To install this firstly remove the trim from the C pillar and then across the back of the rear windscreen. Oh and that's not muck on the headlining its cos my hands are dry etc from this week so its actually my skin
oh and it was raining hence the wet bit as one hand was wet.
Carefully then pull the headlining down to reveal the bolt holding the antenna in.
Now all you do is undo this bolt (you require a 22mm socket/spanner). Disconnect the wire. Put the other antenna in its place. Connect the wire and fasten up the bolt. Remember only do it up hand tight then half a turn.
End result is
When finished. Carefully return headling back and re attach trim. Took me all of 20 mins and that was taking pics aswell.
Carl