Hello Ian,
As I understand it, E10 has been the norm on the Continent for a few years, and again as I understand it, there hasn’t been many reports of disastrous consequences with its use in older cars. I used it in three 20 year + cars last year, and a bit when allowed during Covid - well they are still running!
I get the impression with yourself that ideally it’s E5 - or nothing - and I think you will have to consider the possibility of the ‘or nothing’ bit, since fuel stations are unlikely to occupy one tank with much slower selling E5.
Again, I think it’s been justifiably pointed out on here that E10 is ‘up to’ 10% Ethanol, and doesn’t necessarily mean the ethanol content is consistently at that maximum.
Just a thought.
Kind regards,
Gareth.