Didn't make the call because by the time I got it all apart and cleaned up, it was just about 5PM on the east coast, so I'll call tomorrow.
It looks like the brake pipe from the flexible hose to the caliper cracked. For all I know, I kinked it two years ago when I put in new swivel balls, and my incompetence came back to haunt me. I'm just hoping the part I found on the web site will work on a UK spec (RHD) caliper as well. I'm assuming it's the one with imperial measurements, because the 12mm wrench was too big, the 10mm too small, I've never seen an 11mm wrench, and the 7/16 was a Goldilocks fit (just right!). As far as the threads go, well I don't have a gauge that fine.
As always, this has led to other problems. The (alloy/tapered) lug nuts are supposed to be 27mm, but the 27mm wrench does not really fit (including the lug wrench that came from Solihull 'way back in '98. This leads me to believe the caps come off, but I don't think they do. One socket is still attached to a nut, so I'll be ordering one of those as well. I've heard that the wrench not fitting is a sign that someone used the wrong sized wrench once... And that's likely happened over the last 26 years or so. Heck, I don't even know if it's supposed to be 27mm or 1 1/16. Most of the fasteners on the car are metric, but there's that 7/16 on the pipe, so...
There does seem to be a tool to remove the cap from the lug lock. What was interesting to me about that is it was still in an old plastic bag with a barely legible part number on it: ANR3496. This does not seem to resolve in any internet searches, but ANR3196 does. That however is a blanking plug for a receiver hitch, and my UK spec hitch has no "receiver".