mine was already pretty damaged by the time i got the bike and had some major problems getting it out for a long time
it had clearly been done up WAY too tight because after setting up a socket and extension with i think it was a 6mm bit on the end (i went for the biggest bit that could get grip on the damn thing) and it took all my strength and then suddenly there was a massive SNAP and i practically fell flat on my face, fortunately for me it was only the socket and extension falling apart as the drain plug finally moved for the first time in years
i havent had any problems undoing it since then and am careful to do it up as tight as possible (without causing further damage of course)
my bike came with quite a few hideously overtightened features (it took 3 guys and a very very long socket extension to get the rear axle nut undone) the real b*ch of it is i just noticed ive lost yet another bolt which i can assume vibrated itself loose and slowly undid itself then made a break for freedom, i think i will have to invest in some of that loctite stuff