Big-les you are a hero, many thanks for taking the time to post the details for fixing the clock problem.
I had the clock problem on my newer 5 year old 9200 hummy (my other 7 year old one is still fine!) and did the cleaning thing using Electrical Solvent Cleaner from Maplin. I got rid of some dirt on a few cotton buds but I still had the clock problem.
For others in such a situation, don't panic. I then took it all apart again and unsoldered that capacitor that I'd cleaned round. I cleaned the board underneath where the capacitor had been and then the capaitor itself and resoldered it back in.
Bingo, that did the trick and I had my standby clock again - job done! Brilliant, and not very difficult at all for a non-expert like me.