Rust and wear (wear shows as grooves on the pin) make hinge pin removal difficult just like kingpins on the front suspension.

You want grease where parts move against parts. Grease makes the parts last longer. When the hinges and pins were new, the grooves helped to hold the pin in place, so grease is not necessary at the grooves. Some greases evaporate/decompose over time so periodic maintenance is needed. I've seen clothing spotted by brushing up against a hinge so the grease that may last longest may not wash out of clothing. On a farm, where many of these trucks were used, the farmer selected whatever oil/grease he/she had at the time and applied it in the easiest/quickest manner possible.

"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."