There are a number of things going on here. In case you don't know, the knurled nut is the speed fine-tuning adjustment for the motor. That needs to be screwed onto the threaded shaft so the motor sits almost level. It isn't part of the bearing at all.
You are missing two parts. One, a solid metal disc and a c-clip. if looking at the bottom of the bearing shaft (i.e.: the end the platter shaft enters is at the bottom of your view) the order is this: neoprene washer, derlin disc, solid metal disc, c-clip. All three parts should be small enough to fit into the shaft, but big enough to hit the shoulder of the bearing and not fall into the well. The C-clip locks all parts in. In an original 698, the thickness of the o- ring, derlin disc, metal disc, and c-clip are such that when all are installed properly, the c-clip *just* fits into the groove that is in the aluminum bearing housing to form a tight seal fit.
The bearing uses this type of c-clip:
You
should be able to get non-Empire OEM parts that will work. My guess is you'll need to replace the parts you have. The derlin disc is probably worn and the other side of it, if it isn't smooth and clean (no scratches) should be replaced. If it's smooth and unblemished, you can just make that side the part the tip of the bearing contacts. The o-ring looks trashed. I'm not sure what the sizes/thicknesses should be though. Maybe someone else can chime in with that. Replacement derlin discs are available on ebay, but I don't know if they are correct in size and thickness.
