I then took the 4 small screws out and removed the small cover from the top of the unit. Looking down inside I could see where the shaft went through.
The outside of the aluminum body was covered with a good coating of corrosion (aluminum rust?) so I surmised that that's probably what's applying the brakes to the shaft, so with some wishfull thinking I put a small amount of pickling vinegar (7% acetic acid) down in the bottom of the housing, just enough to cover the shaft.
It didn't take much persuation to get the float arm and shaft to work smoothly and easily after that.
I then poured the vinegar out, flushed it 3 or 4 times with tap water, then a few more times with distilled water, gave it a blow job with low pressure compressed air and put it out in the sun for a few hours to dry.
24 hours later it's still swivels nicely, but not too loose.
Good old VINEGAR, that's what did the trick, so it's not just for chips.
Just thought I'd pass this along, for what it's worth.
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