Hello vintage Omega experts and enthusiasts!

I have an Omega from 1969, no, it's not the moonwatch, but rather a 14k gold filled Seasmaster De Ville. It is a ref. KM 6292 in a case made by the Ross company in the US. It has a cal. 563 in it.

Currently, the crystal does not fit properly on the watch. It was on the watch when I purchased it from a thrift store last year, but it seems to be too large or the ring is not correct. The crystal makes a loud squeaking sound when you press down on it. It's also an aftermarket, non-Omega crystal.

Would anyone know the correct type of crystal that would go on this watch? I would love to get a genuine Omega crystal if it's possible.

Anyway, here are some pictures!