Thanks for the reply. I'm not sure if it's aluminium (not there at the moment). I will check. Is there anything that can be done to treat this if it is aluminium? I was hoping I could clean the deposits off and then smear vaseline over the mechanism.
I've just moved into a beach front property. The windows have a sliding mechanism to inhibit them opening completely and this is all encrusted. I don't know if this would be calcium deposits? Would something like Limelight be a suitable treatment for them? Any other suggestions?