machine got stuck trying to drain water for 6 hours before starting a
wash cycle, hope it didn't damage the drain motor. However...

i could see water was being pumped out of the dishwasher by looking
into the waste disposal, flowing fine so no blockage in drain...

incoming water pressure confirmed OK, by disconnecting incoming water
pipe and flowing into bucket...

removed baskets and spray arms & started removing plastic parts from
inside tub.
removed plastic tube which feeds water to both spray arms (2 torx
screws). then removed small plastic cover on LHS of drain sump (1 torx
screw). this exposed the (i think ) drain impeller, which was turning,
not quite freely, but in a way that tells me there is still magnetic
force between the rotor and stator of the drain motor.

also exposed is a small black rubber object, which was gunged up with
powder; removed that from its position inside a narrow slot with a
screwdriver, and it's actually a little flapper valve with a round
seal about the size of a nickel. cleaned off the powder, rodded the
drain port with a bottle brush, and flushed the drain a few times with
hot water. slipped the seal back in its slot, put everything back
together, and cycle advances normally. BINGO!

Not sure about this, but I think the flapper stops water coming back
into the drain sump (the drain pump can't get ALL the water out, some
will inevitably remain in the drain hose between the flapper and the
air-gap) otherwise the float switch will never drop down telling the
machine "ok im drained, go to next step". So if the flapper is gunked
up, not sealing, water is coming back in from the drain hose as fast
the pump is pushing it out, so the float switch stays up, so the drain
keeps on pumping.

Would anyone care to speculate on any damage which the drain motor may
have suffered by running for 6 hours straight?

snip
Would anyone care to speculate on any damage which the drain motor may
have suffered by running for 6 hours straight?

I'd have to say seizure. And, as it's running, nothing is wrong.

Someone else had the same exact problem in this ng a while ago as well. IIR