4.8 not included? I have an 05 4.8. I thought it had basically all the same potential issues the 5.3 could have. Mine is leaking from somewhere, I can't exactly tell for sure it's the rear main. It also has a couple leaking valve seals. Going to m1 0w40 seems to have dropped oil consumption slightly. It was down about half a qt when normally it would be over 1qt low. Still monitoring to confirm but that and the oil pressure didn't start to drop at 2500 miles are my observations so far.Neither oil is going to stop or slow down a RMS leak. This is very common on the LSx engines. Especially in the 5.3 and 6.0 variants.