I Had a chat with Mark Longmore today, ha cannot supply new diffs but do not worry if yours needs fixing, the chap at Grantura Engineering is the main man in the country for the repair of these, he rebuilds them as standard and with different ratios etc. for Morgan and Marcos ( whom they still supply ) TVR's etc.,
they were the same as ours apart from the ratios and parts will always be plentiful

The oil is critical in these, only 3 makes can be used ( see previous post) they spent £ 25000 signing off these oils, many others were tested but failed, the diff is robust but you can get problems if repeated ( 25 or so ) 0- 60 runs are carried out as they get hot and the oil takes a pasting with little free flow of air, if you do track days change regularly .

as for the ones that came from the factory Mark Longmore had a look at these as the receivers wanted them to buy them back !! there were 30 or so but some had appeared to have been dropped so they backed off

When these diffs were new an additive was added that contained phosphate to help run them in, this should have been changed at 1000m ( has yours been changed ?? ) then any swarf ect gets changed and you can then leave it in for 60K miles

Mark sees many cases where so say specialist gearbox & diff repair centres
try to repair and set these up and get it wrong, also using other oils that are good in other aplications and tell you marvelous things on the label but not good for our cars, Dreadnought also sell the correct oil I believe.