Which type of Royal Purple?

[Darius]

Royal Purple has a transmission fluid for manual transmissions specifying GL-5 and GL-4 transmission fluids (Max-Gear) AND it has a transmission fluid for manual transmissions specifying automatic transmission fluid (Synchromax). Which one is best to use in a manual RB25 transmission? I'm assuming Max-Gear, but please correct me if I'm wrong.

[Carl H]

you need gear oil for a mt that uses gear oil and with a gl-4 rating, gl-5 will eat your syncros.i use redline mt90 in my rb20 box and it works a treat.

[Darius]

Do you specifically need GL-4 even if the label says, for both GL-4 and GL-5?

[mugengsr]

when synthetic gear oils like redline and royal purple say gl-4 or gl-5 for example the max gear . its rated for the gl-4 and gl-5 that does not mean it acts like a dino based gl-5 ... and eats syncros .. it does not have the same sulphers that dino oils have so it does not react to the brass in the syncros .. so its safe : )