Could be fun with a pair each side!

I've found Wych Bearings to be very helpful in finding o-rings if you give them the measurements and use. Brake fluid is a harsh fluid though. Possibly ring Wabco in Buckingham, UK, although you will need the measurements as they threw all their drawings away years ago.

You have a Dixie airhorn?

Yes, it looks possible to get a hand in from underneath but not much room. The RAVE method is to remove the battery and then its tray!

The modulator can be a total bar-steward to get all air out. I used an Ezibleed kit when I replaced mine and flushed about 3 litres of DOT 4 through before pushing another 2 litres through the lines themselves. Front lines are usually OK. As Brian says, rear lines are almost certainly shot if...

I'm seriously beginning to consider just fitting an air-horn setup that plays Dixie!

You can't. It is part of the horn. Looked at doing that first.

If you want reliable then don't look at any Range Rovers. Buy a Lexus RX.

Actually, looks more like the standard waterproof one.

Just remember groved side goes on a grooved pulley and smooth side goes on a smooth pulley.

Got a spare horn on the scrapper but not sure if it works.

C196 it is. More likely to be a Superseal. At that price it might be worth a shot.

There are two connections on the new horn but no plus or minus or earth symbol. One side might have 06 stamped next to it.

Seems to be OK. Nothing above the wheel arches. Bit of a mystery. I'll have a more thorough look next time I am under there.

I wonder if you could get away with some clear-setting epoxy from a modelling shop with a dash of wood dye in it?