servis quartz 600 drum problem

I have a servisquartz 600 which I bought in 1982 and over the years have replaced bits like pumps motors brushes belts bearings etc. But recently I have had vearious clothes marked with rubber , possibly from the non original door seal (which does not feel as sliperry as the original) and some burn marks. I have noticed that the inner drum seems to have gone eccentric and with unbalanced loads touches the outer drum and sparks which makes it hot at this point which is obviously causing the burns. I checked for play in the bearings and they seem ok. How the drum has gone eccentric I dont know unless a severley unbalanced load caused it. Can I straighten it somehow or does anybody know where I can get a second hand inner drum? PS if anybody needs info on error codes I have the original handbook.