That is EXACTLY your problem. The tensioning belt isn't tight enough any more and as the tape rolls it goes slack. When it stops at EOT, it folds over itself, and often creases the tape, creating a bad spot that you hit on every pass. I have had to replace 100+ belts as I've been reading all of my tapes. Pretty much any tape from the mid-80's earlier will have a bad belt. Sometimes they're so bad they snap on the initial retension (you do know you have to retension the tape before you try reading it, don't you?) Scotch DC450+ carts from the early 90's have been my primary source of donor belts. The bad news is the piles of surplus carts that were all over Silicon Valley in the late 90's are pretty much all gone now..