A Result!!!!!
Good news from Garmin. I wrote pointing out that I though it unreasonable for my Pilot 111 to fail so young and for me to be charged for replacement, and did they think they had correctly assessed the situation.
Today, a free replacement Pilot 111 arrived in the post.
Result!!
Thanks to PPRuNers for telling me of your experiences with Garmin, and for encoraging me not to just accept that I'd be ripped off.
Thanks to Garmin for taking the reasonable stance.
SSD