okay, so ive mannagd to get some of that oil, and ive put it in

just taken for a test drive and it has improved the clunk a lot... however it is still there slightly in first and second gear ( it doesnt knock and clunk about when i engage the clutch even when im not being gentle. it just makes one quiet knock...., it is 100% diff related though. the thing i wanted too make sure of was that the diff bracket hadnt torn away and those welds were fine... all looks goood, I think its all bush related though. I need to explore and understand the diff more though. It looks like there is some slack on the output drive shafts that go to each individual wheel... but i dont really understand where exactly the slack is, wether it is in the diff or later on in the drive train... i believe it to be later on because when i turned the shafts individually i could feel it and there wasnt instant engagement of the diff... im not sure if this is normal or not though..... as i said im not well up on car mechanics so please excuse my lack of knowledge.
i may be wrong and it may just be another bush somewhere in that area... its a bit of a guessing game though as its such an old car and mine has very very little service history.
mines a manual and im pretty sure its not clutch related as the sound doesnt come from there.