I have a Mirador 20X spotting scope that I use for high power shooting. I have had the scope for over 25 years. Every time the humidity gets high or a rain storm comes along my scope starts fogging up to the point I can't see through it. It fogs up on the inside. I understand some scopes are sealed with nitrogen to prevent fogging? If the seals go bad and the nitrogen leaks out then can fogging up start? What would be the most practical fix for the scope? We are not talking about a real high dollar scope here. Thanks to anyone who can give insight on this.