Glass port scratches are as problematic as they are inevitable. Fortunately, it is possible to remove scratches in glass ports if the scratches are not too deep. Stephen Frink suggested to me I use "jewellers rouge" which I found on Amazon. I used a Dremel which has a power cord (when I tried with battery packs, ran out of juice before finishing) and a whole bunch of felt polishing wheels (catalog #414). It took a long, long, long time. Perhaps an hour but the minor scratches did disappear. I went through a number of felt wheels. It is a long and boring process but gives one time to reflect on the dangers of rocks attacking poor defenseless dome ports and to be more protective in the future. I write this now as I am preparing to attend to another session of polishing, which I hate as much, if not more, than cleaning the camera's sensor (also necessary this weekend). While you are out diving and having fun, think of a tiny wheel spinning round and round and be thankful if you have acrylic domes how much easier they are to repair.
I can't guarantee this process will work for everybody but so far it has done well for minor, hairline scratches and little dings. I hope this advice cuts into the sale of replacement Seacam domes, Harald is doing far too well these days.
For those with damaged Subal glass ports, please be aware that they can be returned to Subal for replacement of the glass. While far from cheap, it is considerably less expensive than buying an entire new port.