You might need a rebuild. It really sounds like you might have blown a seal OR your seals are dryed up. Your right at the predicted mileage for one even though your is N/a. From the sound of it, it is your seals since you operate fine at high-rpm this is usually the case sinc rotaries can blow seals AND continue to run hard as long they are above 6-7k rpm depending on the engine type/port. I'm assuming you since your is N/A you probably have the six portand not the 4. Now before I jump to conclusions do this...
1.Get some good non-sythetic tranny fluid (1 bottle at most).
2.Pour the tranny fluid in the engine (a good amount on both rotors)
3.Just crank the engine over for a good 10 minutes or more but don't try and start it... -> You might have to manually turn it over.
4.Let the fluid sit/soak in the engine for about a day or so.
5.After a day or so try and start that bastard up, this should work if you don't need a rebuild. It will also unleash a HUGE cloud of smoke if it works.
6.Let me know how it goes
Why do this? Tranny fluid moisturizes the seals and gets them to expand in a sence. My mechanic taught me to do this on an Fb (1978 Rx7) that sat for 5 or so years. And yes this does work.