I have similar problem on my 2001 WRX. Engine misfires and has been sitting on the driveway for a few weeks while I try to fix it. Last time it was idling on the driveway, mostly firing on all cilenders but occasionally only on 3 of them (misfire codes on all cilenders) we noticed vapour coming out of the oil filler cap on every piston stroke. And the vapour smelled of pure petrol. Just checked the dip stick now (a couple weeks later) and it is about a quarter up the stick and smells of petrol.
Did you find out what your issue was / and does it sounds like mine could be the same?
Iām currently thinking I will need to rebuild this engine but hoping for an easier fix