I've had these 2 Siamese cats for the past 10+ years.  Though they both
eat the same dry food (and that's about all they eat), one of them has
always had the problem of dropping a single roundish turd here and
there.  Either I'm getting more sensitive or my furniture is getting
more expensive so that this problem has started really annoying me or
she is actually doing it more often.

Not a full-on poop, mind you.  One single roundish turd.  She seems to
involuntarily drop it while sleeping or while in the ecstasy of a
full-body petting session.  I find them often where she's been curled
up sleeping and I see her do it much less frequently when I'm petting
her.  I often find 2-3 each day lying around where she's been.  She
does also seem to have pretty regular full bowel movements like the
other cat does.

Possibly related and equally annoying is that she often has a moist
butthole which leaves stinky marks if she sits with her butt down on my
lap.  I don't notice it on other things as much as I do on my pants.
The other cat does not have this problem.

She is mostly in-doors, though she goes out once or twice a day for a
little while.  I've tried a variety of different dry foods, some wet
foods (seems to make the problems worse), and haven't noticed much
change.  It seems to almost be a psychological thing (anyone know
Freud's take on anal expulsives?) and not a digestive issue but I could
be wrong.  Maybe a weak sphincter?

Any tips or anyone seen this kind of scatalogical behavior?
Thanks,
bmart