Nice machine! That was my first Sanitaire. I picked it up at Goodwill about seven or eight years ago for $10. This seems to be a somewhat rare model. In looking for parts and reading lists of models here on Vacuumland, the SC686 seldom appears. Fortunately, I've had 100 percent good luck with parts for an SC886, and even used some of those spares to fix up my S645 (blue professional series), which I acquired later. Yours seems to have had good care. The brush roll has been upgraded to a VibraGroomer II. Mine came with the original VibraGroomer, but the bearings were shot, so I similarly upgraded mine.
Unlike you, I hate dump bags, so I converted mine to an F&G setup. I've still got the original dump bag, minus the spring at the top, which I needed for my S645. Otherwise, it's in really good shape. If you want it, it's yours for the cost of shipping. Just let me know. I shook it out as best I could when I took it off the machine but any original dirt remaining inside will be included at no extra cost