I believe you are talking about the clutch assembly. Go to this link and see if were talking about the same thingPictorial: DF520 Clutch Assembly w/ part numbers
In the second picture, you'll see the bracket bearing assembly which contains two bronze bushings inside and an oil hole outside for lubrication. Part number 9433763
Sometimes if the burner worm shaft rubs on the side of the hole where it goes through the cast iron base of the fan assembly, it will also squeal. This can be caused with the worm rotating unevenly in an off-circular pattern because the gooseneck bushing or worm bushing is worn out. I think many of the DF520 parts are interchangeable with the 350.