Correct compression? Rocker shaft end float?

I've also seen numerous reports on the rocker arm needle bearings wearing out and becoming noisy. It's not clear if the shaft ruins the bearing, or vice-versa. But it's clear that SOME rocker arm issues are out there.

Listening with a stethoscope is the first step.

We had this at a tech-day once!  After much sleuthing we found one adjuster screw thread was buggered from previous adjustments.  Even though we had valves set and adjuster nuts locked they would vibrate loose almost immediately with a running engine.  We just backed out the adjuster then used the existing lock nuts (like a tap/die) to carefully straighten out the threads, very small turn of nut then back it off, then same tinny bit more, until threads are straightened. Then we reset that valve with no further issues.  Lesson Learned: Check the simple stuff first.

Sounds like a failed rocker arm bearing/shaft assembly. I'd begin by checking rocker end play; it should be as snug as possible, without binding, about .001" to .003". Excess end play is often a clue the assembly is failing. Since it requires loosening the head bolts, I'd remove and inspect both assemblies on that cylinder, and probably the other cylinder as well. When an assembly begins to fail, the arm starts to wag excessively, which causes rapid end play. On the shafts, look for brinelling, and replace if even mildly discolored. No need to remove the bearings for inspection; look closely at the bottom of each bearing cage for cracks or chipping. Always replace an entire assembly; upper and lower bearings and shaft. When installing new bearings, pay attention to proper end play.

If a bearing cage has chipped, as described above, the needles will work their way down and out of the cage, then exit the rocker assembly via the slot in the lower trunion block, then down into the oil pan. No cause for alarm if you find some of the needles missing but, at a minimum, change oil and filter, and insure you have a magnetic drain plug, to monitor future oil changes. The needles usually just lay on the bottom of the oil pan, and you can remove them if/when you ever have other reason to remove the pan. But if you're squeamish, go ahead and drop and clean the pan now.  

In reassembly, use the appropriate shop manual to set rocker end play; earlier Airheads are simpler, by squeezing the trunion blocks together while snugging the head bolts. Later Airheads use shims, but either works well, and end play usually wears very slowly.  Hope this helps.