Another update to this story.
My hope that replacing the old pads with the new ones was going to be a quick job was shattered yesterday morning when I discovered that the caliper wasn't sliding on the pins properly.
One of the pins slides in the metal body of the caliper but the other one is housed in a rubber boot which pushes through a mounting on the caliper. The pin sliding in the metal housing was fine but the hole in which the rubber boot is held had become oxidised to the extent that it was compressing the boot and gripping the pin, thus preventing any free movement.
It took me a while to realise what was going on initially, but once I had identified the problem it was a simple matter to gently extract the boot, clean all the white oxidisation out of the mounting hole and then put the boot back in with a liberal smear of red rubber grease both inside and outside the boot. Both pins on each caliper were similarly treated and then the whole lot re-assembled with the new pads.
The job also gave me the opportunity to flush all the old brake fluid through and replace it with new fluid. My brakes are now working possibly better than at an time since buying the bike four years ago.
