I have found that even modern grease will work its way out of the spring shackles, kingpins, tie rod ends etc. I usually try to give these items a shot of grease every 1000 - 2000 miles or so. Every time I do this, the steering and ride is a little better. This one fact tells me that frequent greasing is required due to the original design.
I will also note that I put new spring bushings and shackles on my truck about 20 years ago, and when I replaced my springs recently, the old components were still good 'n greasy and like new (other than the cork seals at the shackles.)
So my opinion is to keep up with the lubrication schedule and use modern lubricants. I do agree that the engine oil drain time can be significantly increased. But even here, because the engine is "open" -draft tube and rocker arm cover vents in many engines- A more frequent change is advisable.
Kurt
