VW Shark-fin aerial

Hi ho. Right, I have an Octy, and I have asked in the Octy mk1 group and it was suggested that I venture in here....., so here goes:

The aerial on my estate seems to be playing up. I have a Pioneer headunit fitted. In conjunction with that I have a power injector powered from the HU (blue wire). This has worked fine for a number of years, but couple of weeks my radio reception become very poor.

Initially I though the power injector had failed, so I bought a new one from ebay for £5 and fitted it the other day. The results might be a little better, but not as good as it used to be. I mentioned this at work, and someone said they had a shark-fin from a VW/Audi (in a previous job he used to fit hands free kits, etc). I assumed it was a "proper" VAG part.

Does anyone know if these are a straight swap for the factory fit aerial in terms of the hole in the roof and the cabling? And plus how much are they worth, or should I just try and source another amplified (standard) base for my normal aerial?

I do sometimes use a roof rack, so having a short aerial could be a bonus, as long as it works (don't like the look of the S2000 ones - tooooooo tiny and toooooo "chav" looking for me!)

Anyone fitted one and got some pics - ideally on an estate.

When I looked on ebay for a few earlier, some seemed to have a trailing wiring, which I guess was to supply power the amplifier in the base.... however as mine has a power injector behind my headunit in the dash, I assumed the aerial base would just take the coaxial feed and extract the power internally? Or is there a box that sits on the roof lining which breaks the power out?

so either:

headunit -> power injector -> coaxial cable -> amplified aerial base

or

headunit -> power injector -> coaxial cable -> breakout box -> coaxial + power feed -> amplified aerial base

Cheers,

Matt