Found out about this problem here: Neck Melt!
I feared this one very much since, I knew Fridart would come with an SBH obitsu body.
This particular obitsu body has some kind of content in its neck that can melt a pullip's head!
I mean seriously! ヽ（゜ロ゜；）ノ
Oh well.....I guess no doll is perfect. Even the great almighty obitsu has some "issues".(；¬д¬)
When Fridart arrived, I knew I would have to expect some melting issues with her....and alas, I was indeed correct. (ノдヽ)
Of course I needed to prevent the obitsu body from further damaging my $100+ worth of doll....that I work so hard for.
I used this Tutorial: Solve melting neck part!
Its not that hard! You only have to change the teflon tape when you needed to.....I suggest, checking the tape once a month.