Keys sticking, and it was seriously interfering with practice. I had a shufty on YouTube. I took out a couple of the offending keys, and also non-offending keys, and compared the felts as per what this bloke says. But they didn't look any different... So, not thinking really, I just pushed the keys from their ends, towards the body of the piano... Eue-bloody-reka! Absurdly simple, intuitive, effective. Voila.
And then I got back to a sticking-key-free practice. First few bars two hands. This is great fun - I'm playing it well, and it sounds lovely with two hands, it's just v-e-r-y s-l-o-w. Unlike southern parts of the UK, SW Scotland's very wet and forecast to continue so. Which, encouraging us to stay indoors, means I might get right through it two hands this weekend, and can start to speed up in the week.