It has (had?) an oil separator for the engine breather tube(s) and the oil tank. If it's still there, it is a little plastic container, about as big as a coffee cup, under the battery, above the front "U" part of the swingarm.
Is the #4 still sputtering? Often, riding these awhile will smooth off the carbon that collects on the valves, making the engine miss if it hasn't been ridden often (and fairly, umm...briskly...). I've also found that splitting up a can of BG44K into 5 or 6 "portions" for a series of gas tank fills helps to clean these off, too. Compression goes back up afterward.
How's the charging system doing? Do you have OEM type coils, or maybe some 3-ohm type instead? The latter can drag the battery voltage down when ridden for 3-4 hours in slow traffic.
After I restored the K8 on my patio the later "K" bikes have grown on me somewhat. I still think the "F" tanks do look a little better on them, though, even if the K8 tank can get you halfway across Colorado on a single fill! That's kinda important out here where fuel stops can be 100 miles apart...
