I'm thinking of doing my timing belt, I see there are different kits. I understand its a good idea to change the water pump since your in there, but some kits have front and rear cam seals. Do they need to be changed when replacing the timing belt? Or only if leaking? Also the R has about 50,000 miles but the belt is 8 years old, I know I'm good on the milage, but does age play a factor in replacing the belt?