I had same issue with similar Olympus 720. You might try soaking it for a while first, but I just removed the front face plate. There was accumulated gunk holding the lens cover. Gently wiped it all clean and presto! all good. You are not opening the camera, just removing the front face to clean around the lens cover so it can slide.

I don't know if the 725 is different, but on the 720, there are three small allen screws on the front and a small phillips screw on the edge. You will need a very small (1.5mm) metric allen wrench (found in common allen wrench sets), and a very small screwdriver for the little screw on the side (found in common micro screwdriver sets). Keep track of which hole each allen set screw came from, they are all different, in fact one appears to be just decoration and has no threads, I just secured it with a tiny dab of all purpose adhesive (Ace hardware brand). Check the tab near the lens goes back in place. Dr. John Christensen

P.S. 720 looks exactly the same as the 725 so above should be worth a try.JGC