I didn't take the time to read all of the above replies, but as far as I know GHB doesn't "melt" plastic.
As for GBL, YES IT DOES. I wouldn't really call it "melting", but it does "take a layer off" if you will. There are little "accident dribble" marks here and there on shit like CD cases, the top of my expensive TV, bit on my leather cell phone case (dunno why it reacted there), I think a bit on my car where the window buttons are, etc. (hehe, don't ask)
I also remember doing the same thing you did the first day I got it. I put a small bit in a plastic tube thing they use for holding coins or whatever and when I got to this party and was sucking the shit out with a syringe to measure it out, the "plastic, white, sticky, jizz-like goo" started clogging up the needle and making a hell of a mess. This was just straight GBL though.
I suppose if you got shitty GHB and it wasn't made correctly and there was still GBL left over from the reaction you could still get some of the melting effect, but I'm no scientist.
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