300E Heavy steering on r/hand turn
 

Hi,
i have a 300E Mercedes Benz that has heavy steering to the right. I had this steering box apart about three months ago and resealed it, only oil leaks. (I am a qualified mechanic.) It has come back now with heavy steering to one side only. I have pressure tested the pump and have 1500psi on l/lock and only 500psi on the right. I have removed the box again and dismantled it, i cant seem to find anything wrong.I must be missing something has anyone come accross this before? Any help would be appreciated, even a book or something.

Kind Regards
Ross