Hi There,
I've popped the back shrouds off and the cabin air filter to try and see quite what's what. Gosh it's busy!!! Why they didn't set the break fluid reservoir more to left in the big spare space I don't know!
Seems to be a couple of pipes under it that may be accessible. There's also the big funky flow solenoids block on the right and that's fairly buried and right next to electrics too which mean popping hoses could be fun!
All this not helped by having an LPG install adding more hoses, wires and stuff to move!
Am almost wondering if it isn't easier to flush the whole radiator system???
There's mention of a heater bleed valves
#61
https://www.audiworld.com/forums/a8-...2859358/page7/
Though predominantly American forum, and the location of things do tend to differ???