have a look at the state of the belt, they will stretch as they get older.
Mine had actually started to crack between the grooves in the belt, so had the power steering belt!
Haynes manual is rubbish, if you go to the adjustment section, it tells you to go to another page, then another page, then back to the 1st section! All without telling you anything!
That guide i posted is your best bet, used it to change thermostat and it has the all the belt paths in there a well