Just an update to whot happened. Got an answer from
sales@onyxboox.com. The warranty was not valid (13 months), but they would repair the screen for $100 + shipmant cost one way. i agreed and got the device back today (actually a new device). the total cost for me mounted to around $200 (including $50 fee from customs when I received the device).
It took 2 months, but can-t complain on the result. They kept their bargain after all, but had to nag to get information about progress.