From having a gritty diff no matter how many times I rebuilt the thing following step by step guides on this forum. I have now solved the root cause
What happens when you tighten the diff screw is pressure is applied to the two bearing faces before pressure is placed on the balls and diff rings. Either the two bearings don't seat correctly or the bearings are slightly too thick. I have replaced one of the bearings with a thinner type 5x8x2mm instead of 5x8x2.5mm. Hey presto my diff is now super smooth and is easily adjusted.
Try this...
Split the diff
Remove 1 bearing
Reassemble the diff
Set up diff in accordance with guides on other oople posts
Note you get the diff working with only one bearing!
Now do above but insert 5x8x2mm bearing.
Worked for me
Good luck
Please respond if this works for you