John,
I'm running Jessie on two of my three Raspi's. I have one of each model, th e model 1 is in a robot, the model 2 is running a weather station and the n ewest model 3 is used for Python programming. I used to this on the model 2 as well as run the weather station to create additional graphs and reports against the weather station database.
As soon as I got the model 3 I did a clean install of Jessie on both the mo del 2 and model 3. I also took the opportunity to install the latest weewx weather station software and then restored the database and config files fi le from backup.
This morning in a rare moment of clarity I tried lxappearance on the weathe rPi and it's there and works fine.
There is something not right with the model 3 as I'm definitely getting the command not found error.
Earlier today I decided on a format and clean install.
Having backed up my python files I reloaded the copy of Jessie I used befor e and installed it to my newly formatted SD card.
Everything looks exactly as it did before but now lxappearance is working j ust as it should and having swapped to 'Adwaita' I now have a proper border around the drop down menus and they are a lot easier to read.
I also did an apt-update and an apt-upgrade to bring it up to the latest ve rsions and everything is still fine.
I have no idea what caused the problem or why but it's now fixed.
Thanks to everyone who responded.
Nick