There are places that sell compass repair kits but probably for about the same as a secondhand airpath compass. I had a leaky compass in my homebuilt and it was just as cheap to buy a secondhand, non-leaky compass.
I suppose it will depend on what you operate and maintenance legislation as to whether you can do what I did or even repair it. I don't have any details to hand but if you need more info then PM me and I'll try to dig it out.