Omega Seamaster Cal. 500 Crystal

Hello, A good friend gave me his father's Seamaster. The crystal is yellowed and I'd like to find a new one. The crystal measures a hair under 30mm on the outside. I took the case back off and it reads "Patent # 315.164" Under that's 2846 2848 and under that it has a big 3 followed by a small 3C. Without taking the watch apart and popping the crystal out, can anyone help with the correct size crystal I will need?. Otherwise, it keeps pretty good time knowing it hasn't has a service in probably 40 years and has been sitting in a drawer all that time. I took an early 60's Omega Constellation to my local watchmaker and he charged me $160 for just the crystal (says he got it directly from Omega). I thought that was a little much so I thought I'd try to find a less expensive crystal this time before I give him the watch to be serviced. Thanks for any help.

You need a 5140 glass.
https://omegaforums.net/threads/crown-glass-gasket-list.81619/

Thank you very much
J

Which numbers on the case back are significant? How do I decipher the numbers. I know what all the numbers on the back of a vintage Seiko mean but I'm un-educated what the numbers mean on an Omega. Which is the case number, etc?

Google

Thanks, I'd like to learn what all the numbers mean. Is there source material on how to understand Omega numbers? Thanks
John