Go for a k&n one. Re-use able and better gains. Spoom one is too dear for minimal gains!
Today my new gearbox arrived, an oem ek9 s4c as my car has the longer s9b box in it, not sure what happened to the original gearbox in the car but got this for a decent price.
Been told it crunches when high up the revs in 3rd so guessing it is needing a synchro. Not sure the best place to get replacement ones are as these are double syncrhos in 3rd? Any information is appreciated.
Try some honda mtf 3 as a first resort see if it improves. Gearbox oil has sorted out a lot of gearboxes I've come across.