I've got an old Farallon compass that doesn't work too well because the fluid's leaked. It has a refill screw in the back, but I'm not sure what to put in it. I let a few drops out and it felt more like oil than water or spirits. Does anyone know what I should refill with? I was planning on draining before refilling just to hopefully get some of the gunk out, but I'd rather not end up with bubbles one liquid inside a different liquid when I'm done.