Turntable Bearings

To answer your question, one must first determine the value of the table in what you believe it's current condition to be. I sounds as if you are somewhat confident that there is/could be an issue with the bearing. At this point, walk away there are many many of these LP12's in various states of condition and upgrade on the market. You can buy a LP12 from a dealer as mentioned for as low as 2000.00 that he would have gone thru. I know Rick would not let a "problem prone" TT out of his shop. He may and will suggest upgrades as that is a dealers path of business to LP12 owners. As far as what will fit the oldest LP12, anything Linn produces will retro fit their LP12's. They never have changed the base units, just keep adding upgrades,e.g. motors, bearings, suspension, arm boards, tonearms, power supply's and the list goes on. As a former owner I decided to move in another direction as the desire to upgrade would have been too expensive. But with out know what dollar figure you are looking at on this particular LP12, it is hard to justify if you have to turn around and spend 1300.00 right away. If you could buy a ready to go and properly tuned table for 2000-2500.00 I know where I start.
All my opinion of course. But from what I am reading, you seem very concerned about this table's bearing and, I have found my fears/concerns are usually warranted. If you are hearing something that doesn't sound right, it probably isn't and LP12's are a expensive when trial and error trouble shooting them.
Again just my opinion and no intent of offensive content.

When was the last time you had your 30 year old LP12 serviced or tuned? That would have a MUCH greater impact on the sound than bearing wear. Perhaps, time for new springs, grommets, and a suspension adjustment.

Thanks; The table was last serviced about three yrs ago but it sits on a shelf and doesn't move and I'm very carefull about it's use. As for the upgrade path; I wanted to install a Cirkus bearing last November but it seems I was a couple weeks too late and the 1st. gen Cirkus was discontinued and the new Cirkus was introduced. At significant price increase. I want to state that I don't question the quality and improvement in sound the new bearing would provide; I have heard one mounted on an older Linn like mine. I'm borrowing a binocular microscope from a friend. I'll keep this forum posted regarding my personal opinions and findings; FWTW.
I would like to establish here that this is fun for me; learning these things. And thanks for all the help from everyone.