After trying different size o-rings on return p/s line where it is secured to rack I determined the line had a pinhole leak where metal horseshoe shaped plate secures it to rack due to corrosion (wasn't easy to find). High pressure line is steel and low is alum.! Bad design!!!!!!! Also GM sells a seal kit (2 o-rings) for $30-$40 and NAPA sells same o-rings for 30 cents each! Got everything together today and no leaks!!!!!! Line was $105 at dealer. Hope this helps someone in future.