Getting ready to do 1st start on 818 with 2002 WRX donor obtained from one of of our vendors. Redid water pumps , belt, but left oil pump alone.

Can't get it to show any pressure on oil pressure gauge with sender in sandwitch adapter mounted to oem oil cooler. Tried several times cranking as long as 30 secs.
Plugs out so cranks fast. OP gauge works. New STI oil pan and pickup. One would think of missing o ring in pan but I believe I did that correct.

Any one else have long cranking times to get oil pressure. I know g-rotor pumps can be fussy. Ideas??

Thanks