then the bubble reappeared. It was awhile ago so my memory is a bit hazy, but I think if you remove the rubber cover there is/was a little rubber plug that you can use to fill. When I did it, it wasn't long before the bubble reappeared, so I gave up. A compass repair tech might be able to fix it, but it may not be worth it since a new one is not that expensive. I recently got a new/almost new one on Ebay for about $50.