Put in fluid without first fixing the leak, and you're just pouring money
down the drain. Put in the wrong fluid (some are similar to kerosene, others alcohol, and whatever you use if the viscosity is wrong, the compass will swing about too quickly or slowly as well, even if the numbers don't dissolve off the dial) and you've trashed a compass.
I' a firm believer in DIY but you are best off contacting the maker, to find out what they can do for you. Some will swap it for a new compass, at a significant discount. Others will sell you gaskets and the correct fluid for a refill, or even tell you what fluid you can use.
But to just randomly put in fluid, without matching the type or fixing the leak? That's just a kludge job, if you've got no other way to go.
Binnacle compasses tend to be big (6-8" ?) and that makes them expensive. Also makes it easier to read them more precisely, and to know they are on the centerline of the boat. But any kind of compass, wherever it is convenient for you (not near metal, not behind where someone sits...) will work.