The scratch is really close to the edge of the lens. If you manage to align the scratch with the top center or lower center position of the lens into the housing most probably you can get the scratch out of the field of view of the sensor and if so it does not mess with the pictures
Leak Sentinel / Mico is the way to go!
I bought 2 systems from him.
One complete for a friends Ikelite housing (version 4). It works fine.
Another bought was a standalone valve and pump for my Aquatica housing. The Aquatica housing had the surveyor already, that is able to measure the change in the pressure, so I just needed to add a valve. I do not like the valves from Aquatica, backscater, ikelite, nauticam as all of them are on L shape or too bulky and it seams to me that it is more probable to get things stacked there.
Besides that, it is less expensive!
The surveyor from Aquatica is possible to be bought stand alone. It has the Benedict that also has a moisture alarm, signaling by light and by sound. The draw back is that you need to open the housing to activate the survival and then proceed with the test.
The leak sentinel allows you to activate it without opening the housing, and it allows you to make the test in the day before and switch off the sensor till the few moments before the dive, allowing some saving in the battery.