I have some Val Max Life Syn ($1.75/qt average) from the old AZ syn sale. It's good stuff, but should I try to exchange it for GC at AZ. Last time I was there getting free Techron w/ rebate, I checked and they have GC with 05 and 04 date codes. I have not counted lately, but off the top of my head I may have between 16-26 qts left. I have 8 qts of QS 10-30 SYN also. It's label only specs API SL, compared to the ValMxLfSyn's multiple ACEA specs, and BMW, MB, and VW long life specs. The QS Syn seems weak to me! Should I exchange the QS instead. I got it for $1.50 a pop. If I exchange the 8 QS's thats $12 for $45 worth of GC. Your thoughts please! Any one use GC in older or newer Modular 4.6's or newer Vortec 5.3's?