In June of 2003, I bought my Volvo 940, with 39K miles. Since it was nearly ten years old, at 40K, to prevent problems, I had my mechanic replace timing belt, tensioner, water pump, and front seals. At 90K, I had the same work done. Currently, the car has 120K miles. I have planned similar maintenance at 140K.

Last night, while reviewing my owner's manual, I noticed recommended timing belt replacement is 50K for the B230F/FT engine and 100K for the B230FT with EGR. Why the difference? Am I having unnecessary work done?