How often should I or do you change the transmission and differential fluid if one is using synthetic?

I am going to be putting Royal Purple Max-Gear in soon with new crush and fill washers.

The manual recommends every 30K miles (or X months), but that is with the stock fluid. Do I follow the same schedule with synthetic?

Thanks!

I change mine every spring before track season.......

hmm, I've got about 20K on mine....I'll probably change it soon. Oh, and Royal Purple ROCKS...

you probably *can* go longer on synthetic gear oils (same reason as motor oils), but i think sticking to 'regular' replacement schedule would be fine.

30k max, even for synthetic.

15k for low mileage driving or tracking/auto-x

Crush Washer Info (http://www.rx8club.com/showthread.php?t=44584)

Crush Washer Info (http://www.rx8club.com/showthread.php?t=44584)
One of the many useful and crucial posts/threads on this Site.

Thanks for the answers so far. I didn't know if I treated synthetic diff and manual trans fluids the same as synthetic oil in that I can go longer intervals between changing.

Most likely it is fine going longer intervals, but it looks like sticking to the 30K mile schedule is a good bet. I don't autocross or run tracks very much so that really isn't a factor for my 8.