Comes as part of the louver, just like the rear side vent grilles.
BTW, on my '86 FJ60 project vehicle I harvested rear side vent grilles from my '84 FJ60 parts vehicle, my '89 FJ62 donor vehicle, and my FJ60 project vehicle. Out of those there were one each uncracked left and right vents, several decent gaskets for each side to choose from, and no good flaps on the vent tube inside the rear pillar. I pulled the best two gaskets, which had hardened almost to the point of being brittle, and soaked them overnight in a 4:1 solution of isopropyl alcohol/oil of wintergreen. Softened them up nicely (but they swelled up a bit) and was able to loosely attach them back on the plastic grilles (spray painted the grilles first with Testors One Coat Lacquer, 1849 Graphite Dust). After a day or two the gaskets shrunk back to a tight fit around the perimeter. Meanwhile, I cut out new flaps using thin rubber coated paper gasket material from NAPA and restapled them to the vent tubes. Bothe pair of vent tubes/grilles/gaskets are now back on the '86 FJ60, looking practically brand new.
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