Waterproofing my tv dial constellation

Hi all, Im new to the forum and new to the world of Omega watches, though I've been collecting other brands for a few years now. I have recently purchased a 'tv' dial constellation circa 1973 and although I am otherwise very pleased with it, it has a very annoying trait of letting in moisture very easily.
Having a closer look it appears the only real seal on this watch would be on the lower surface of the crystal? Should a new crystal do the job of making it water resistant again or should there be another seal around the case between the lower and upper sections? Or perhaps I'm missing something else entirely?
All advice, including where to buy a genuine crystal would be very much appreciated. Many thanks, Mike

Generally moisture will come from the back and in that case you need a new seal. Got a pic of the watch ?