out of my mind's inner depths, i just remembered a problem i had with my 2000 caravan.
it was similar to the OP, but it involved all of the turnsignals.
sometimes they would work as they should, sometimes a random corner wouldn't work, and that side would blink fast [indicating a "bad" bulb], sometimes nothing at all, not even the interior indicator lights.
i chased that mess around for quite a while, but every time the issue occurred [in it's various forms] the 4 ways worked, indicating the wiring and bulbs were ok.
i even tried a new [known good-different] multi-function assembly.
turned out the cause all along was the flasher assembly, and of course, it was a dealer only item.
$48.00 later, all was well again, and lasted until i junked it years later. [the flasher now resides in the glovebox of my 99]
i don't know if this IS the OP's cure, but something maybe to look into.
if you could borrow one to try, i would do that first before buying one. they might be available on line now, dirt cheap, but when mine was acting up, it was dealer only.
your mileage may vary. just my experience.