GM started using positive seals on the Vortec heads. Mostly for emissions benefit. Older heads need some lube on the exhaust. The intake seals will determine oil use the most tho. Vacuum on intake side, pressure on exhaust, most of the time.
Check for excessive valve/guide clearence when you change seal. Just try to wiggle valve sideways with no spring load/pressure on it. Should be no movement on a lubed stem.