Rear end and brake wear help

[Pont406]

I swaped to 5 lug disc brakes on mine 69 c10. Today I took the axles to machine shop. While rear is apart I inspected it. Spider gears have some strange wear. Looks like a wood warm groves. Is that a normal wear?
Rear brake parts were replace 4000 miles ago. New drums, wheel cylinders, hose, hardware and shoes. Shoes have a lot of heat cracks and missing chunks. What's a problem here? Maybe it's a new material they use to make them now? I have a lifetime warranty on all these brake parts.
Axles seals and bearing are ok, no leaks. Should I replace them while it's apart? I am afraid to replace them with less quality parts that are available out there.