stick with o-rings. the studs stretch when they are hot... which means you arent getting the "true" torque on them. put your truck throught a complete heat cycle without high boost and let it cool completely back down then re-tourqe. that way you get that gasket somewhat seated then clamp it back down nice and tight.

what do you guys mean by a heat cycle? like drive it around easily until the thermostat opens and closes once?

yes.

i have a 23cm housing and it spools instantly