This backglass does not look like a candidate for sealing. Consider spot touch ups instead and keeping the backglass in an area where there aren't sudden temperature variations. And, keep the machine away from a window and direct sunlight. Applying any sealer to a backglass will devalue the machine and compromise the originality of the machine. It's best to monitor the condition of the backglass, and if the condition gets worse, consider all restoration option first before deciding to "seal" the backglass...