update: sadly, it did not work. I sent it in for service, and it came back in a timely way looking like it had been tested, or so the accompanying letter said according to Google translate (it was in German): but alas as soon as I switched it on, the stripes were there. I don't think I should blame them, as in my own experience it could go looking fine for days, and then start going bad, especially after it had not been used for a while, so it may be that the "rest time" in transit did the trick, i.e. they did not see the problem.
So sadly these are the last days for my beloved 360, and with no 5 inch from pocketbook, I think I'll have to migrate to a Kobo mini. I did see an announcement of a new 5" device from pocketbook on the Russian/Ukranian forum, but it is a vague post on something happening next summer, so I am not holding my breath. Though if anyone has any news, glad to hear it!