i bought a bottle of mineral oil at a drugstore ($1.74) and a bottle of odorless mineral spirits ($7.00 a quart).

i opened up the compass and shook out the remaining compass fluid into a clear plastic container.

i put some mineral oil in a clear plastic container.

i put some odorless mineral spirits in a plastic container.

then i compared the three.

the compass oil was thicker than i had expected, not 'runny' like water. the mineral oil was thicker than the compass oil, the mineral spirits were thinner.

so i mixed some mineral oil with some mineral spirits until the consistency was about the same as the compass oil. then i used an eye dropper to put the mix into the compass, overfilling so that all the air was driven out. then i replaced the screw.

compass seems to be working fine. only time will tell if it is a good solution. if it isn't, well, at least i know how to do the job now.

by the way, the reason the compass was leaking was that the o-ring on the fill screw had deteriorated. i cleaned out the remnants of the o-ring with a pin before refilling.