The fluid in most modern compasses is Isopar, a synthetic fluid available from most compass providers It should be placed under a vacuum to remove any air bubbles. This in turn allows the fluid to absorb any minute amounts of air entrapped while refilling.
The most common problems causing air bubbles to appear in the dome are a cracked rubber diaphragm
or a crack in the plastic dome. The diapphragms stiffen and crack with age. This is not a do-it-yourself job for most people and some compasses ( like most Plastimo) cannot be repaired. Some very old compasses (like C. Plath) were indeed filled with a mixture of grain alcohol and distilled water
A good source for rebuilds is J. Gordon & Co. in Annapolis
, MD. Call them at 410 263-0054.