There was a thread a while ago on this subject but it didn't reach any conclusion so I e-mailed the new makers of my old brass Sestrel compass and got a helpful reply in minutes. The fluid can be an alcohol/water mix (in which case a drop on a bit of paper evaporates) or it's a light oil called Bayol 35 (which has a smell). Mine is the latter and the stuff costs £12 a litre plus p&p etc. Two questions. What would happen if I tipped out all the fluid and replaced it with baby oil? If I buy the litre of Bayol I will use about one percent of it so does anybody want some?