changing the oil in my diffs

[Smed]

just bought a used buggy (Mugen MBX5) and got a great deal on it. but since
i didn't build it, i dont know what oils the previous owner used in the
diffs and shocks. i already changed out the shock oil but now im wanting to
tackle the diffs.

any suggestions as to what weight i should use? 5000 on front, center, and
rear? mix it up? 5000 front, 7000 center, 1000 rear? will there really be
that much of a difference?

what i want to use the buggy for it racing. im not going to kid myself and
say i plan on beating the best, i just want to get the most out of my money
and have fun. money isn't too big of an issue, but i dont want to waste it
buying 3 different types of diff oil if the difference is unnoticeable.

thanks.

smed