Nissan Repair: High oil consumption, crank case vent, oil consumption

Question
Carried 2K4 Sentra 2.5 SE-R back to dealer at 10K miles with check engine light on. Dealer changed intake manifold out. Said studs are bad about working loose. Walmart changed the oil the same day dealer changed intake. Since have had terrible oil consumption problem-3.5 qts in approx 2500 mi. Went unnoticed until oil light flickered a few times. Added another .5 qt after about 250 mi. driven. Had oil changed again due to having been run low. Engine runs smoothly with no unusual sounds. No smoke or signs of leaks, have not pulled plugs to check condition. Dealer service dept wanting to blame low oil level on Walmart oil changers.  My gut tells me something went wrong with manifold R/R. I am not a mechanic and have even less knowlege about how the intake works on DOHC as relates to oil passages. Any thoughts?  

Answer
If the crank case vent tubing is routed wrong or they left a baffle out it would allow oil to get sucked intot he intake and that would cause high oil consumption.  A car with 10K on the clock should be honored by the dealer.  First, get a certified letter from the Wal Mart store to show that they did the oil change correctly.  Then go back to Nissan and voice your concerns.  Have them perform a compression check to verify that the rings are in good working order if they cannot find a hose or baffle missing or installed incorrectly.