I'm feeling it's time to move on from my 2005 5.3 Envoy with 298,000 kms. Regardless I am exploring all options. I pulled the valve covers and noticed the problem. The cylinder 7 lifter was collapsed. I am most likely taking it off the road but want a reasonable fix as it will run in a demolition derby. I'm thinking at the least some b12 Chemtool or equivalent down the rods to taking a chance on a straight up used, lower km heads, cam, lifters, rods, rockers swap. Opinions? Thanks