Replacing everything associated with the timing belt, as in the water pump, oil seals, idler bearings and drive belt tensioners, is very important for reliability. We say the parts you skimp on will come back to haunt you--making the service not reliable or more costly later when the engine has to be opened back up.

It seems the trend lately is the manufactures are going back to the use of timing chains instead of belts. These are not designed to be regularly serviced and do not operate the water pump which can still fail independently and is also not part of a time interval maintenance.