I am a little confussed. Is his genitalia out constantly? When they go through puberty they will have it out more but it retracts. Is the genitalia black or dry? Is it swollen?
Also, at 6 months they should not have baby fur? Have you noticed any over grooming of the tail? I am wondering if what you are seeing is the new hair growing in. If you haven't had him in for a vet visit, I would encourage it. Also, this would be a good time for neutering if you are not going to be breeding them.
Hopefully this is just a coming of age issue and nothing serious. I will be saying prayers. I am very sorry about your other glider, its never easy to lose one of your pets.