2 major concerns RE: rotary engines and oil is that (a) carbon deposits on the apex seals, and (b) certain oil blend will cause/contribute to apex seal chattering, which will scour the inner walls which will lead to failure (loss of compression).
Used to be (well into the early 90s), R.E. Amemiya has their own "house blend" of 10W40 specifically for Mazda rotary (no longer, dunno why).
However, Idemitsu still makes/supplies them:
http://www.rotorsportsracing.com/performancetuning/idemitsu.htm
RE: here in NA, back when Ford has stakes in Mazda, they exert a lot of control over the oil to be used across the board. One of the things that (I subjectively believe so) is the wrongfully enforce the idea of using 4-cycle reciprocal engine oil 5W20/5W30 onto Mazda rotary RX-8, which ,many of them lead to premature failures due to the 2 mentioned failure modes. Although most of them ended up being warrantied (rather unfairly) and a new/remain engine being installed, frankly, I think it's all to do with the wrong type of engine oil being used.
I've said it before and I'll say that again: rotary engine is a different beast compared to ordinary 4/2-cycle reciprocal engine. For that, oil requirements for rotary engine shall be different.
Failure to observe these fundamental differences between a rotary engine and reciprocal engine, and the lack (disregard) of proper lubricant used are what gives this otherwise ingenous design (rotary engine) a bad rap.
Q.
also remember this: lubricant oil blended especially for rotary engine use can be semi-syn or full-syn, depending on the blend/requirements. Ultimately, it all serves the 2 main purpose of keeping the apex seal clean(deposit-free) and free from chattering. DO NOT, under any circumstances, substitute with ordinary 4-cycle internal reciprocating engine oil for it does not possess any characteristics to serve a rotary engine's needs,regardless of whether it's syn or no syn.
