Progress report: yes, much progress.
The final use of the original HDD was interesting; a 60-minute programme resulted in a 52-minute recording. When viewed, there were several gaps and several other periods when the picture on playback was badly fragmented. That led me to realise that an occasional past problem with picture break-up on recordings was very likely another manifestation of the failing HDD. (We are about 15 miles from Sandy Heath and have a good signal; problems with live TV are very rare).
The new 1GB Seagate HDD went in a few days ago; all very easy, formatted very quickly, in only 3 or 4 minutes, to my surprise. We have now had some days of satisfactory operation, including recording and playback, but there seem to be a few residual issues.
First, startup sometimes hangs after the standby button light changes from orange to blue, but before reaching the stage of displaying the Humax logo on the screen. Off/on has, so far, resolved the problem.
Secondly, the TV sometimes restarts on Ch250 (BBC Red Button) irrespective of the Ch in use at shutdown. As far as I know, I have not done anything to provoke this.
Finally, when I used the CF interface for the first time a few minutes ago, a warning of HDD possible problems flashed up - not what I expected with a new HDD. So, I have attached a copy of the SMART data.
Any comments on these points would be appreciated.