I also now know why there is an indicator stalk and flasher relay but no indicator lights: Fenchurch was made in the brief changeover period between when trafficators were discontinued and separate yellow indicator lights were introduced. It has a magic silver relay box that flashes the (red) brake lights and the (white) side lights when you operate the indicators. I plan to change it to use separate yellow indicators instead, as flashing red/white lights are likely to confuse other drivers almost as much as trafficators would, and they'd probably confuse the MOT test examiner too.
I've had a closer look at the radiator and I think I might have been wrong about the pinhole leak. The corrosion may have been caused by water leaking from the top hose and accumulating along the bottom edge. The top hose is definitely knackered but they're very cheap to replace. I've managed to bodge the drain cock shut, and a new one of those is only a couple of quid too. I'm going to get a new top hose and then try running it under pressure to see if the radiator really is leaking. If it isn't, then replacing it can wait a while.