It seems I'm finally able to get my hands on a (very rare to find in market) Greek siren. This model is a circa 1965 hand operated VILMA. It works fine, except some noises heard from inside (?) I hope nothing is wrong with the gears.
The problem is that some screws are heavily corroded and I'm afraid I won't be able to open the stator cover unless I have it machined. (I would prefer not to) Also I cannot remove the hand crank in order to open the back cover to inspect the gears. Take a look at the pin that holds the crank to the axle.