I have bought a 1964 Stainless Steel Geneve manual wind watch, which I am very happy with - except the case back is not firm - it snaps into place but can then be rotated. It does not have a gasket fitted and this loose fitting makes me think it maybe should have one. Any advice gratefully received. I am an absolute novice with Omega watches and bought this one to wear - as I like it and my 1987 Omega Deville Quartz is finally threatening to give up the ghost after 32 years of hard service.