When a dry seal is new, sometimes it will leak more than the allowable limit (two cubic foot per hour per inch of shaft diameter) it can be fixed by gradually increasing the pressure and running the agitator until the leakage comes back into the correct range. If a dry seal leaks after running for a time, the nitrogen lines need to be checked for leakage and soapy water sprayed on the top of the seal. If the soap bubbles, then the seal is leaking and the seal cartridge must be replaced or sent back for rebuilding. If this is an OptiSeal, then a rebuild kit needs to be installed. Dry seals that have been in service for more than a year and show an increase of nitrogen consumption should have the seal cartridge replaced.
When wet seals start to leak after running for a year or two, the cartridge must be replaced. If a wet seal leaks shortly after being put into service, it must be removed, all O-rings must be checked for nicks or cuts and the faces checked for scratches. The O-rings can be replaced. If the faces are scratched, then the cartridge should be returned to the manufacturer it was purchased from and the cartridge replaced. If no damage can be found, then the seal can be re-installed, paying close attention to assembly details. For both types of seals, the shaft runout must be checked at this time to make sure the agitator is running within acceptable parameters.
In short, if the seal is new, then it might be able to be repaired, but if the seal has been running for any appreciable time, then the cartridge must be replaced.