Vintage DD turntables. Are we living dangerously?

Dear Peter,
I suppose we should take this discussion of my problem off line, since it IS rather boring to most.  However, I am grateful for your interest and your input.  The screw-in plug at the base of the bearing well on my unit is very firmly locked in or glued with some off-white substance that is hard enough to resist a screwdriver.  I have never touched the adjustment. Nor did JP when he worked on my turntable. It's quite possible I am looking at factory goop or their version of "loctite", applied more than 30 years ago. Further, the shims under the three screws that mount my motor in the chassis are also apparently factory original, and I have never had a problem with platter rubbing on the surround in the past.  JP reports the same, based on when he had my unit at his shop.  Further, further, two days ago, the rubbing noise was definitely, without a doubt, coming from within the motor assembly; I was able to reproduce it by holding the motor in one hand and hand-turning the spindle, whilst the platter sat off by itself on a shelf.  Last night I shimmed the motor up further so as to eliminate any chance that the noise was due to its rubbing on the surround, even though my common sense told me that this is not the problem.  The finding is that when the weight of the platter is on the spindle, the noise, although fainter than two days ago, becomes audible (last night).  When I add the SAEC platter mat, the rubbing noise gets a little louder.  Thus I can only think that the weights pushing down on the spindle are making the problem more audible, but the problem is probably not due to platter rubbing. Tonight I will investigate with my stethoscope to determine more accurately the source of the noise.  Finally, there is some advantage to my having gone to medical school; I own a good stethoscope.

Don't take it offline. We are interested.

 try this Lew: flip the table upside down and hold it. You'll feel the motor drop down; flip it right side up. Let it settle and then run it to see if the noise persists. That has worked for me before.

That screw we are referring to is actually a hollow cup into which they put some kind of plastic material.  A bearing ball rests on top of the plastic. You can see a pic of the ball on my system page. I conjecture, assuming there is not something terribly wrong with your motor, that the bearing ball is not properly seated on the plastic--that's why flipping it can help. How it became that way is anyone's guess. It may have something to do with the condition of the oil supporting that bearing ball. If the well is bone dry then then your finding that greater weight on the spindle leads to more noise makes sense. For all we know, the noise might be the ball grinding away dry against its plastic seat.

But get in there and see what's going on. In addition to relubing the ball (even though my platter spun smoothly, the well was more or less dry, it spins much more smoothly after a relube), you'll want to check on the condition of that plastic seat and of the bearing ball. I don't know whether anything can be done to replace the plastic (maybe Peter, with his fabrication skills, can make new ones for all of us :) ), but that bearing ball can be replaced with a SiNi one. I've done it and so has Aigenga iirc.

Lewm
  I second the recommendation to remove the bearing nut and inspect
the oil condition along with the  [plastic]  wear plate.

In other tables the wear plate is often changed due to dimpling
and the resultant change in tolerance. 
 

Totem et al, I would not be surprised if wear on the thrust plate has everything to do with my problem.  Tonight I removed the motor entirely from the chassis.  Then with the motor on my workbench, I was indeed able to confirm my hypothesis that pressing on the spindle while spinning it could reproduce the rubbing noise.  With my stethoscope I can pretty much say for sure that the rubbing is NOT coming from the bearing per se, however.  It's coming from frictional contact between a circular gray metal disc at the top of the motor structure (the first thing you see if you remove the black motor cover) and the green circular PCB that lies directly underneath the gray disc.  The green PCB is fastened to a brass platform by 6 screws. I perceive that pulling up on the spindle also pulls up on the gray disc; they're attached as one piece.  This creates enough space between the gray disc and the green PCB such that the noise goes away entirely.  Thus, I think the "cure" for this is to gently turn the screw at the bottom of the bearing well in a clockwise direction so as to push up on the spindle, because of its contact with the thrust plate, and create enough space to cancel the rubbing.  Any comments on this idea would be appreciated; I am not sure of the function of the gray disc/green PCB arrangement.  However it seems they must together form some sort of sensor for speed, because the pieces are not nearly hefty enough to be the stator and rotor, which I can see reside on levels below this top tier.  If they are a sensor element, then I fear the possible problem that might arise from upsetting their spatial relationship.  I sent a photo to JP and Peter; I haven't the time right now to post the photo on the internet so I can cite it here.

At this point, I see no absolute need to mess with the lubricant. Unless someone has an opinion to the contrary and a reason to back it up.