I don't believe that they can be repaired.
There are lots of people selling repair solutions, but they are sealed units when new. If you think about it it is not just a question of removing the mist/water inside, it is finding the tiny leak which has led to the unit failing. No matter how much you dry out the unit, unless you find the leak the problem will reoccur.
What I do is find a supplier of sealed units who will deliver. New sealed units are not as expensive as you might think. (E.g a small top window sized unit might be ~£10.) Delivery costs can be higher than you would like. I wait until I have several which need to be changed. This brings the cost down. I have changed loads myself and I'm no DIY expert.
Jim, March 2018
