Thanks all for the thoughts so far. ( The oil is a controlled rust prevention system that most old cars develop ). I must admit to being concerned at the advice that if we don't understand what it's for throw it away. It must have some purpose in preventing end thrust on a bearing that is not designed to have it. It is very adjustable - if overtightened it would heave the engine/gearbox rearwards and presumably knacker the diff input shaft bearing. Is there anyone out there who understands these cars? David