Are you working on the same machine you discussed in your link? I didn't read the entire thread, but I gathered that you are trying to eliminate unexpected motor noises after the vacuum sits unused for a while.
My experience has been that the culprit for such a noise is usually the ball bearing, not the brass sleeve bearing. I know it's always tempting to try to lube or replace the sleeve bearing (because it's cheap/easy, right?) but after doing so, I find the unwanted noise usually persists.
The best solution I have come up with for addressing the noise, then, is to either lube or replace the sealed ball bearing. On Hoover vacuums, this usually involves drilling out the rivets which hold on the steel retaining plate and replacing the ball bearing. Simply drill out the rivets and slide out the bearing.
Now that the bearing is free, you can pry off both the rubber seals, blast the bearing with break cleaner, dry it thoroughly, re-pack it with high-temperature grease, and press the seals back on. This will fix the noise, however you still can't "roll back the miles" that were put on the bearing--it will never be as good as new. Much better is to simply go to a bearing shop (or shop online) to buy an identical replacement for only a few dollars. If you look hard enough, you will spot a combination of a few numbers/letters on the bearing. This is the bearing's "size." It is standardized; you do NOT have to buy a "Hoover" brand bearing. Hoover doesn't even manufacture their own bearings. They simply buy from a bearing supplier just like you.
Popping in a brand new bearing is the way to make it work like new again. Now simply find suitable rivets or screws which can re-fasten the lower bearing retainer plate and...voila! Smooth operation again!
See below for some pics. I have done this to my Concept One U3317, and I suspect the same can be done for you Convertible. I put in a brand new sealed ball bearing and three new blind rivets. Washers were added as reinforcement to keep the rivets from possibly pulling through the bearing retainer plate as I installed the new rivets.
Disclaimer: Attempt this only if you are sure you can drill out the rivets without ruining the base or bearing retainer plate AND if you are sure you have the correct hardware to re-assemble everything. You do run the risk of ruining things if you do it wrong, however, if properly executed, this service produces great results. I know it sounds like a lot of work, but if you have the right tools and hardware, you can get it done in a matter of minutes.
Good luck, and let us know how it works out.
