Olympus OM20

Hi all, first visit here for a while since the “new look”! I’m looking for some advice regarding my Olympus OM20. We’ve had it for around 25-30 years, and it came from the boot of a police car in a carrier bag full of water and sand. My dad cleaned it up and it worked flawlessly for years. Until now it hasn’t been used for probably 10 years and I have been given it! Because I don’t have enough cameras!

Playing with it the other day I noticed that regardless of whether it’s switched on or off when operating the film wonder the shutter is released, this happens 90% of the time and it’s never happened before.

Is this a common thing with these cameras? Not sure whether to open it up and have a look or whether to just put it on the shelf as an ornament