First of all, I'm pretty sure the diff and tranny see a lot more abuse than the internals of a rotary engine, but I could be wrong. Its just that from everything I've seen GTX provides plenty of protection for the engine. If I remember right my engine (with 215k miles) was actually OK as far as the bearings go when it was torn down for a rebuild. Sure they weren't great, but they were far from failing and my e-shaft looks good as new. Considering it probably didn't even have oil as good as GTX 20-50 for most of its life, I think that regular oils would be fine.
Don't get me wrong, I agree that RP is better, its just that I don't think its needed in most cases for a rotary engine. That said, if I have a high-dollar rebuild or raced my engine then I will most likely use RP, but for most engines I just think its overkill.

Cheap synthetics do not burn as cleanly as even the cheapest regular oils, so yes, that is true.

I am glad Rotary God is here to set things straight. I read his (and others') posts here and on RX8club when I was "researching" the synthetic vs. dino debate. I am convinced and will be using RP once my engine is broken in. The most convincing arguments are:
* Rotary God's comments on what Yamaguchi told him
* Idemetsu oil used in the 4-rotor is synthetic
* Info on Royal Purple's website re: use of synthetic in rotaries
* Pineapple Racing likes synthetic based on how good the rotor housings look when the engine is torn down for rebuild
* It makes sense that Mazda would issue a blanket statement rather than qualify and disqualify certain oils and open themsevles to a lawsuit

They carry RP at corporate NAPA stores and at Pep Boys.

Would it really protect the housings better? I guess I was only thinking about the bearings and such. Shit, if it really does protect the housings better then I'm all for it. Of course I'm pretty sure I'm just gonna premix anyway from now on. Oh well.

Dont know if this is worthwile of posting in this side of the forum (first gen owner here), but I run RP in engine tranny and diff. Love it, I went from regular ol' Dino oil though, but the car seems happier.

yeah agree.

if you are going to use RP do it because u want to not because of there "dyno" they did.....

sorry if u have seen the video u know what I mean.. they take a car dyno it drain out the engien oi, diff oil and trans oil fill with rp and dyno.. the numbers go up.... OF COURSE THEY WILL they drained used nasty oil... now if they would have drained it did a test with clean fresh reg oil then drained and with rp it would have been a better test

Dave

btw mazda has a writen letter of acknowledgment for ELF synthetic oil in the rotary engine

Tranny and Diff oil lasts a long time. I'm with Sideways7 (actually across the board, because I use Royal Purple in my diff and in the tranny, and Castrol GTX 20w50 in the engine). If you change out your oil every 3000 miles, are you really gaining any benefit to the Royal Purple? Then, is it enough of a benefit to justify the extra $36 every 3 months or 3000 miles? ($8 vs 2 = $6/qt + 1qt to top off)

I also second what the guy above said about cold performance - with the royal purple in the diff, I've found that if I let the car sit a couple of months, the diff will pop in corners for the first 20-30 miles or so.

Castrol GTX 20W50 yeah!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!