nightmare diff, root cause????

[ASKay]

Hiya, i don't know if anyone can offer any advice, it is not critical as i have got a new diff to keep me going, but would like to repair the old one to sit in the spares box....

I have an SX3 and have never had a problem with the build or running of the SX3 diff...

However my Cougar SV, which was bought 2nd hand has had very little running by myself all of sudden did some strange things....

I ran it alittle at the weekend (a couple of laps pracise) at torch, and as it accelerated it tended to pull to the one side, almost as if i had different levels of grip left to right.....

When i got it home, i noticed the Diff had stiffened completely but also was slipping... so it was almost as if it had tightened.... odd?

I then stripped, and cleaned it.... could not see any blantant signs of wear, but the washers did not look as rasied as i would expect them to be.... but this is from memory of the SX3 diff.

When the diff was re-built and set with the quarter turn guideline, then it would feel right, but when in the car it was slipping so much that i thought the slipper was loose....following this i tightened the diff until it did not slip (progressively, it took about 3 or 4 adjustments) but then the diff is pretty much locked....

So my question is...

The cougar SV c/f pro, does it come with steel diff balls or the ceramic ones?

Is it likley that flat spring washers is the cause, or could it be that I need to replace the diff balls, or even the main 18mm washers?

Any other advice or methods or tell tales for working out what needs to be done....

help or advice would be appreciated