Volvo Repair: v70 2001 intermitting oil presure, volvo dealer, external oil

Question
288k miles ,new oil pump-seals-cleaned pan-cleaned pick up screen-replaced 'o'rings-replaced sending unit for light,attatched external oil presure gauge-either hot or cold the oil presure drops off to '0'.stop the motor,and the presure returns to normal then drops off again!what else could it be,where else do i look?
it was sugjested to flush the motor or to power flush it with a'bilstein'heated power flusher.....i am open for your idea.
regards
scott

Answer
you have to make sure the seals were installed correct did you install or Volvo dealer you need to know how to install seals you can make mistakes easy also you can have blockage in engine oil guides  or you can have bad oil pump engine   flush will not help .did you do oil changes on time every 3000 miles ? the only way to clean it the right way is if you have to much build up or dirt  i is to take engine a part but by that mileage you can get new or used  engine labor to clean that will be expensive