Shitty gear oil is the best. Coastal non-synth ruled my WRX. Coastal synth rules my 240sx even though I'm missing about 1/2 a quart.

Your tranny is fine if it only happens once in a while. When I shift fast, I can feel the tranny spit the shifter out of gear. As long as the gear works, I could care less about the engagement. Especially 5th.