Bennett Price wrote:
I've got a small 12V DC .9 Watt 'muffin' fan (1.75"x1.75"x3/8").
It was the cooler for a video card's processor chip and was
frozen up.

I put a drop of oil into its sleeve bearing and it now runs
reliably - almost. It will start every time as long as it is
not oriented with the open 'face' down. (The open face is the
side in which you can see the bearing). If the open bearing is
down, it sometimes starts and sometimes needs a slight nudge to
get it going.

What's going on? How come? TIA

You oiled it, but you didn't get the gunk off the shaft. When the fan
is oriented face down there is enough endplay in the shaft for the bit
of gunk left on it to bind in the bearing. When it's face-up, that part
of the shaft is likely outside of the bushing.

When doing these, I usually operate them briefly with some kind of
solvent, until they run freely again. Then I flush the bearing with
that solvent--blow as much of it out as possible--THEN relube with 3 in
1 type oil.

Sometimes I also pack the open space with a bit of cheap grease before
resealing...figuring that if the bearing starts to get hot because of
binding, some of that grease will liquefy and and replenish the bearing.
I don't know if that's valid, but I usually get good life out of the
refurb.

OTOH, fans are cheap and readily available...much cheaper than the stuff
they protect.

jak