Your humidor is supposed to protect your cigars from drying out and allow them to age properly. First, you need to make sure that it really is the seal and not some other issue. However, if you are sure that the problem is your humidor, the best way to fix it is to take it to an expert woodworker. Checking humidors for leaks is pretty simple.
To do this, it has to be able to hold in humidity. If the seal on the door is going bad (or has been bad since the beginning), then you will not be able to enjoy your cigars as well as if it worked properly. You should also know that often the problem is not the seal, but the construction materials for the box.
While it takes weeks for cigars to really dry out, there’s no point in taking chances. There are a few things that you can try to fix that leaking seal. The flashlight test is a good one to try, though there are many others out there as well. The dollar bill test is popular, and there is also the tape/plastic wrap test as well. There are other problems that can seem like a leaky seal, but are something different altogether.
Each of these can help you determine if you have a leaky seal and, if so, how badly it’s leaking. A professional should be able to cut new wood peaces for the lid. If you have a clear lid, it should be glass and not Plexiglas. If you do not have a professional woodworker in your area, or you simply need to save some money, you can try to fix the seal on your own. This can be done relatively easily, though the results might not be very pretty. To try fixing the leak yourself, you can get some weather-stripping from your local hardware store or DIY center.
Make sure that they use Spanish cedar, though – pine and other woods do not work in the same way and can cause leaks and allow moisture to seep out anyway.
Install this on the lid and see if it makes a difference. In addition, the wood used needs to be Spanish cedar, and not something else. If your unit is not made with these materials, then chances are good that it is subpar and will leak no matter what you do.