If you happen to scratch your ASI1600 sensor cover glass, as I did recently when trying to clean it, a replacement is readily available from ZWO.
It is not listed on the website yet but you can buy them for $28 (air shipping included). The cover glass product reference is: D32 AR window. Just email Vanessa at ZWO and she can fix you up via Paypal.
How did I scratch it? I was using a supposed clean camera sensor cleaning swab to wipe the cover glass surface and the swab or glass must have had some dirt on it, as afterwards I could see small surface marks in angled light. I guess the best approach would have been to blow it with a puffer first, or just leave it alone.