Update. Took the chain off this morning and gave it a thorough de-gunking in a jam-jar of white spirit, and gave the chain ring and sprocket a thorough cleaning too - so much easier to get things clean with the chain off the bike!
Anyway, I took out a link and tried to fit the chain back on the bike. It was too short, and wouldn't join. So I put the link back (now there's a job I never want to do up a mountain side in a rainstorm) and took another look. Turns out I had made a boob - the EBB wasn't at its maximum extension at all! I had only inspected it visually before, but with the bolts slackened off I was able to rotate it forwards and backwards easily. By watching the chain as I did this it was a doddle to find the
real point of maximum tension, and with the EBB at that point the chain was at a nice tension again. I was surprised by just how much adjustment the system allows. When I put the link back it was a bit stiff, so I had to give it a tweak with a screwdriver. After doing that, and with some dry lube applied, everything seems to be running smoothly (and cleanly
).
Looking forward to taking the bike out for a spin tomorrow, looks like a sunny day.