May be the seal is too big in diameter. Then the small button in the lightseal groove, about just underneath the advance lever, will not be depressed when the back is closed.
Yes, I've replaced a few and if you started with one which was badly deteriorated, you would think the little silver tab should be covered. It shouldn't. I may have directions on how to replace the seals in these OM cameras that I got from my supplier of material. If that would be helpful, send me a PM and I'll try to find them. Bill Barber
I probably should have used 'A light seal Odyssey' like I did when I replaced the seals on the QL-17, but I couldn't find it at the time, once this film is done (can't remove it because I don't know what frame I'm on!) I'll have another look.