Yup! Shim=washers under the nut.
"I can see the blue Thread Locker, too, but I usually keep in mind the fact that I may be the one pulling the damn thing off again in the future..."
If I'm not in my driveway, I'm more likely to have a breaker bar, less likely to have a grinder. I agree that something other than the lock washer should be applied over any shims.
Like I said, if it were
my equipment, and I wanted to use that pittman arm, I'd give shimming a try.
There are a couple reasons to not shim:
First, by stacking washers, you are adding more wear surfaces. Any debris, or surface imperfections that are present when the nut is torqued down, will pulverize or flatten under load, which lets everything move around, and wear, which lets everything move around more... When you take apart a critical assembly that is subject to loading, look for shiny spots. They are caused by parts rubbing against each other. I've heard this type of wear called "fretting."
Second, If the washer's outside diameter is much bigger than the nut, it will be hard to inspect for cracks. By the time a crack in the pittman arm is visible, you might be wondering why your steering won't turn.
So, I guess the ideal shim would be a solid spacer, just big enough, tacked to the pittman arm.