Kenmore 90 Series washer won't agitate/drain/spin & metallic noise

I’ve got a 90s-vintage Kenmore 90 Series (Whirlpool) top-loader washer (model # 110.26914691) which has recently started giving me problems.  I replaced a failed lid switch a few months ago, then it started making a metallic chattering sound during agitation.  Finally, it stopped spinning, draining, and agitating altogether with a buzzing noise.

I disassembled the machine and cleaned everything up with the following findings and results:

I found quite a bit of fine black dust on the floor under the machine, the foundation, and tri-base plates.  I’m guessing this was from the brake, clutch and/or tub wear pads.

Springs are intact but look a little weak / stretched out.  The tub sags a bit to the front-right, especially during spin.  I’ve got some on order and plan to replace all 3 suspension springs and the counterbalance spring when they arrive.

One tub wear pad is missing entirely (front-left) and the other two are worn down considerably.  I’ve got some on order and plan to replace all 3 when they arrive.

Suspension pads are in good condition.

Removed drain pump.  Pump is good, no obstructions, and turns smoothly.

Removed motor.  Motor turns by hand smoothly in both directions.  All windings (start/slow/med/fast) check as good--show expected continuity and >2MOhm insulation resistance.  Some minor overheating on the molex connector for the neutral (white), but doesn’t seem to impact the operation of that circuit.

Motor coupler was worn a bit around the shaft (both motor and transmission sides), but was intact.  I went ahead and replaced this with a new-style coupler with the metal shaft mating surfaces.

When I removed the upper agitator, there were no agitator dogs installed (and no sign of them at all!).  I installed a new set.

I was unable to initially get the inner tub off of the drive block, and the top of the transmission shaft was not as far up as it should be: it looked like the whole inner tub was higher up on the transmission shaft than it ought to be.   I finally got it free by pulling up on the inner tub and tapping down (hard) on the top of the transmission with a rubber mallet.  The drive block was pretty encrusted with soap residue and corrosion, but I was able to clean it up with a wire brush and SOS pads and there was nothing obviously wrong with it once it was cleaned up.

When I went to remove the transmission, the brake assembly and spin tube came out with it.  The spin tube was jammed onto the shaft of the transmission and there was about a 1 to 1 1/2 inch gap between the top of the clutch and the bottom of the brake assembly, such that the clutch spring wasn’t engaging the brake pawl.

I was able to get the spin tube off the transmission by flipping it over, putting the top of the transmission up against the floor and alternately pushing down and twisting on the brake/spin tube until they came free.

I also noted some light scoring around the upper part of the transmission shaft (below the gear teeth) and the outside upper part of the spin tube.

Once removed, the transmission turned freely by hand in both directions, with the back-and-forth action in the agitate direction as expected.

The clutch seemed okay, but I had a new one on hand so I replaced it.  The brake pawl and assembly operated normally and appeared to be in good condition.

I cleaned the soap residue and corrosion off of everything and put it all back together (new clutch, new motor coupler, new agitator dogs, new lid switch), including a light oiling of all the metal-to-metal parts.

The machine now fills, agitates, drains and spins properly.  BUT, there’s still a rather loud metallic chattering or rattling when during Extra Slow and Slow agitation, as well as during Slow spin.  The noise is NOT apparent during Fast agitation and Fast spin.

Question 1:  Any idea what’s causing this metallic chattering in Ex Slow/Slow agitation and Slow spin?  If desired, I can post a link to a short video/audio clip with the noise.

Question 2:  Any idea what caused the spin tube to jam onto the upper transmission shaft and why there was a gap between the clutch and the brake?  Is there something else (drive block, perhaps?) that I should be looking to replace to keep this from coming back?

Question 3:  Anything else I ought to be looking at but haven’t?

I’m quite interested in keeping this machine in good running condition (they don’t make ‘em like this anymore) and I'm willing to invest in doing so as long as it's economically feasible.

Thanks again for your insights and advice!