Thanks guys. I removed mine and fixed it. It did't leak well enough to damage the board seriously. I will now need to buy batteries and a laquer to spray on board to brotect it again, which I washed with white spirit to remove the leakage, which damaged original laquer. I'm going to drive without batteries. I'm thinking to extend wires out of the siren and have battery in another place which is easier to control.
It will also give me a bigger choice of shapes and sizes of NiMh batteries.
Just because I went in that area I also changed the Central locking pump motor.