HDJ 2000 headband rubber melting (sticky)

Hi!!

I have a pair of HDJ 2000 for some time now and I've been using them ever since I got them till this summer because I was offered an HD25 Adidas and I thought I might save the HDJ 2000 for studio purposes. The thing is, the HDJ 2000 were kept inside a headphones bag for half a year and when I took them out I felt this sticky thing in the headband, in the same area where the Pioneer logo is and I don't understand why!

I've read here it might be moisture but that's not the case..

@Gavin, you closed a topic like this early this year: [CLOSED] Pioneer HDJ-2000 Fake?

How did you solve the case to these guys? 

Thanks guys!