Kyosho plastic gearboxes self tapping or machine screws

[alcyon]

I know BITD for my Mid the manual explicitly says to use self tapping screws to hold the gearbox down to the chassis. I am putting in new gearboxes for my LWB mid and cant really decide to go for M3 fine thread machine screws or self tapping as the manual asks for.
Which one will hold the gearboxes down better without causing damage to the plastics. The M3 seems to be gripping well but I worry that it might not hold so well in the rigors of brushless off road competition. Which screws would I be better off with ?

[tamiyadan]

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[EvolutionRevolution]

In both cases, don't crank 'em down more than needed. With self-tapping screws it's quite easy to screw them in too far, causing plastic parts may crack.