I'm currently getting a RX-7 it has about 206,855 kilometers on it and it has been parked for a while now. The owner says "When I parked it, it had a lot of oil blowby"

I was wondering what are the common causes of this in a rotary engine and now much of a job it is really to fix.

 

that means the motor needs a rebuild. The internal seals are bye-bye.

 

It's just worn out.

Then again, it could be something VERY simple like a bad purge valve. If it doesn't smoke with the oil filler cap removed, then it's a purge valve issue.