Well, it gets weirderer and weirderer!
To belatedly answer your question, Brian - its a La Crosse WS2357.
WD has been locally onloading and displaying the data without hitch throughout.
After my update at 22:10 yesterday, I again did a manual refresh and left it (sorry, missed your reply until this morning).
During the remainder of the night, the wx files behaved impeccably, so it looks like something kicked back in. I have been monitoring during the day and no further problems.
The only things not running correctly now are localweather.gif and weatherbanner.gif which refuse to show the weather icon, although they generate each hour and upload each hour - the icon area is blank.
Thanks very much for your help.
Although we didn't get to the bottom of it, it has gone away.
Tony