I just got 30k service done at a local shop for $282 minus oil and sparkplugs change decent price IMO...i had Amsoil in my tranny and RP in diff but after the service i found out they put RoyalPurple Synchromax tranny fluid in my diff instead of Maxgear I asked them what happened they apologized for buying the wrong ones from Pepboys so they said to comeback later and redo the diff fluid only. So is it ok to leave the Synchromax in there until next service or change it out ASAP with Maxgear diff oil??? THANX

 

30K is too early to change sparkplug (unless you have some major mod).

 

I'd have them replace it now. From the RP website:

Synchromax is recommended for manual transmissions that specify an automatic transmission fluid or motor oil.

The 350Z doesn't use AT fluid.

 

The temps are much higher in the diff than in the transmission and you really need to get that fluid OUT of it immediately before it does any long term damage to the bearings, etc.

 

I would change it as soon as possible to avoid premature wear in the diff.