Say münchen86:, I hope you don't mind my merging your few topics, across multiple boards, into one thread. You seem to as the same question again and again, and I'm sorry you haven't had a response so far. I'll try to help get us started, even if this isn't an area of expertise for me.
I would bet the product sold does have traces of other allotropes of sulfur in it, instead of just S8. And if you re-crystallize from the appropriate solvent, the crystals you get will likely be the correct allotrope and crystalline form. Wikipedia says the form is stable, but I do know that sulfur will change its allotropes on its own. So I can't say for sure how long it will last.
I'm left wondering what your exact application is -- how much of a trace of allotrope impurity is acceptable, and why. It may be that your application is too esoteric, or even not possible.