I spent many hours this past weekend doing this - both the wrong (3+ hrs until I quit) and right (1 hr) ways. I thought I'd offer some tips from my experience to possibly make it easier for the next sailor.
The wrong wayQuickly Scan the directions from Beckson and go your own route, thinking how hard could it be. It took me 3 hours to get one seated, or so I thought. My thumbs and forefingers still ache. You will think you have the wrong size. After testing with a cup of water it leaked into the aft cabin.
The right way (follow the Beckson directions)1. Stretch the new gasket all around its circumference as you would a balloon, being careful at the seam area.
2. Start by seating the legs of the gasket somewhere between 2 corners.
3. Once you get a bit of it seated, bend the gasket part away from the channel (where the leg is seated) so that you can get a your tool to seat the rest of the leg. You would hear a snap but you will get some feedback that the leg was set in place. Beckson suggest using a ruler but I used a wooden paint stir stick and it worked great. The entire leg should go into the channel, especially around the dogs, or you will have leaks.
4. You will likely still have to stretch along the way and the last corner won't be easy. when you try and seat that typically another one pulls away. By stretching and re-seating you will finally get it.
5. Note: Back off of the dogs before closing the windows as the new gaskets are not yet compressed. If you don't you could break the Beckson lenses.
My second gasket took about 45 minutes, then I went back to the first and seated my work from the day before using the stir stick. No leaks!
note: You will know when the leg is properly seated as it goes ALL the way in, especially near the dogs and hinges which I couldn't get with my fingers. If you see parts of it showing and you think it will be ok it will not be. You will get leaks and the gasket may pull away when opening and closing the port. The leg is intended to go ALL the way in.
I was confused when I read the directions
http://www.beckson.com/installgasket.html about bending the gasket 90 degrees. I finally figured it was toward the port opening (not perpendicular to the track) and was for the purpose of getting the stir stick to seat it fully in the channel.
Here are a few pics to illustrate. It should be 1 pic but I couldn't take and do at the same time.
Good luck!
Bryan