Thank you for the reply, they are a real relief !
The bike sat unused for some time (been run on and off for 7 years, which explains the low odometer reading).
When unleaded came out I used lead substitute on standard valve seats. Now, I do not use it anymore as French user reported it's expensive and useless * (if you monitor your valve clearance quite often, you'll see it the seats are going in ). I had the valves redone 60 k kilometers ago and the seats where not touched. Maybe next time the valves have to be done, will I ask for new lead free seats...
Now I plan to use the bike more and more instead of my fine and boring Honda. So I renovated the bike to make it look like new. In that process, I've overhauled the carbs and put new floats and new diaphragms. So I expect them to survive the ethanol. (the old floats had still the same weight and floated like the new... )
The tank has still it's original liner and, as far as I can tell, it's still in good condition (no garbage in the tap's filters other than the junk found in modern gasoline... ) I hope it will stay OK for long as the repair liner are not as good as they used to be according to other French users.
* In fact I had trouble geting a very good carbs jetting with the lead substitute. It seems that it interact differently with different brand gasoline. It is becoming difficult to have these engine running fine these days.