Which gearbox fluid

[Kim2000]

I have a year 2000 Jag S Type 3ltr V6 Auto. It has the metal gearbox pan, not the plastic all in one filter type. There is a lot of conflicting info about but what fluid should I use to do a filter and fluid change. Is it mineral or synthetic and can anyone give me an idea of where to get it without paying over the top, which Ive also heard is quite common. Thanks in advance for any info you can help with.