my 02 TD5 developed front axle leaks both sides. So far only the rh seal has been replaced, but it still leaks. Should the tophat shaped collar that fits inside the axle oil-seal be fixed to the half-shaft? The one on my car is loose & can be easily removed. If it should be fixed, suggestions as to how to secure it please, or will the half-shaft have to be replaced?

What make seal is it? You dont say if its a D2 or Defender, but on a D2 only use NAK brand as others are not sized correctly.