he was a great author by virtue of his work 'the Tin drum', but is it known how he could hide his Waffen-SS membership for so long? He would have had a highly visible tatoo on his left arm; did he got rid of the tatoo somehow after the war or was that something that people were keen to overlook ?
SS blood group tattoos were traditionally located under the left armpit, which you could keep hidden quite well. (Unless he had another tattoo that you are referencing.) Additionally, he was only in the SS for a year, near the end of the war and transferred in from a labor battalion, so it is entirely possible that he never had a blood group tattoo applied.