I'll tell you what I learned from reading at The O-Ring Store LLC online. My O-Ring is an 025. An 025 is 1 3/16" ID which is exactly what my old one is as is the plastic cover hatch OD. An 026 is 1 1/4" ID. I ordered Buna N material as Buna N is for fresh water and salt water service. The FKN Viton material looks to be better for chlorinated pool water, but not enough to appear to matter. The Buna N doesnt like continuous sunlight exposure, but when my O-Ring is in place and greased it can hardly be considered bare and open to the sun. By the time it sees that much sun the rubber on my computer will probably rot and the display will yellow.
I bought this exact product - AS568-025 B70 (NBR) Buna N Nitrile 70 Duro O-Ring. Cost was $.05 ea with a minimum order of (13), for a whopping total of $.65. They also had a jacuzzi pump ring. I'm absolutely confident the ones I ordered were the exact ring I needed, but the jacuzzi pump ring looked slightly fatter. Minimum quantity was (1) @ $3. Since shipping was $6 I added it to my order - part number "92200190 Aqua Flo Dominator Trap Lid O-Ring". I probably wasted that $3 but I'm sure I'll recover from the blow.
All in it was $9.65 for 14 rings. I believe these rings will also fit my wifes Oceanic, and also have a friend who has one as well. So I'll probably keep 6 and give the other 8 to Jeff at Maximum Scuba in League City, Tx. Once the rings come in and are installed I'll post a follow up.
The O-Ring Store has sizing charts and a wealth of information available. Hope this helps.