Older fluid filled compasses used either alcahol or a kerosine like fluid. Newer versions use Silicon based fluids. The later versions are better damped due to the higher viscosity of the silicon fluids.
These usually leak less and don't suffer from evaporation because the seals used are highly compatible with the fluid.
You can purchase " compass fluid " by the half pint from outlets such as Aircraftspruce.com for roughly a tenner.