DazzlerRB5

Hope this is the right section...I'm after a bit of advice if possible please. I have an RB5 which once warmed up has a slight jump, on turning left or right, which has been confirmed as the diff.
I'm just wondering which recommended people I should be looking at to have this done? I know there's the option of going for a six speed transmission, but as I'm sure you're aware they seem to be quite rare from what I can see and therefore is reflected in the prices.
My only issue is, I gather the six speed gear boxes are stronger, plus given the extra gear sit nicer on a long journey, from what I've been told, but its still a fair amount of money to spend on a box that I have no idea of the condition of, until fitted if you see what I mean, plus any potential associated dramas should there be a problem!
So my gut feeling is maybe get what I have already rebuilt by a recommended specialist, that or maybe buy a reconditioned unit (unless its sell a kidney money?!)
Given this is probably a common occurrence given the age of these now, what has anyone else done in this situation?
Any help would be very much appreciated.
Cheers