Differential oil synthetic or mineral ?

[Auto]

Hi just a quick question which type of diff oil do you guys use synthetic or mineral ?
I am wanting to get some ordered for my automatic boxes differential I presume originally it was mineral so I'm worried about putting synthetic in incase it reacts with what ever residue is left over from the original stuff , I just wondered if any one has any thoughts on the subject
Any advice welcome
Cheers phil

[Aidan]

Synthetic will be fine, change it again in a year, it's only 1.25 litres and it'll be pretty much all synth and the detergents will have washed out the old carbonised residues