The radiators tend to develop slow leaks between the aluminium core and plastic tanks. Mine has been leaking on and off for 5 years now, sometimes it will go months without loosing any, then all of a sudden dump 500ml in one shot - usually in winter when I park with a hot engine in very cold temperatures. I keep telling myself I'll swap it out in spring but haven't gotten to it...
It's quite an easy job except for the fact the bumper cover and lock carrier fasteners get rusty in our winters and usually at least one of them will strip or break. Spraying them with penetrating oil for a few days before attempting disassembly will help.
There's a good guide for putting the lock carrier in the service position here:
http://pics.tdiclub.com/data/500/Radiator_mounts_install_guide_v2.pdf
Once that's done everything is easily accessible. I use M8 × 150mm bolts from Brafasco to support the lock carrier.
I'd offer to help but I'm not exactly around the corner from you.
Simon