Just to weigh in on the debate (which is probably one of the most vexed in wine-drinking circles) the cork in question may not be a "cheap agglomerate). If you still have it just check whether the 'Diam' logo is branded somewhere on it, always on the side and at times the logo is small and faint.
Home Page Superficially the cork might look like a cheapie but if it's Diam* I'd be more than happy, it also answers the question of how little staining etc is visible as compounded cork closures respond quite differently to natural cork closures when in contract with (red) wine, just my two bobs worth
*they cost the winemaker considerably more than stelvin