Intake manifold question

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So I'm in the process of replacing my transmission. While under the hood, loosening bolts for the transmission, I noticed a bolt was missing from the rear of the intake manifold. So, me being new to engines/transmissions, I asked two different friends about this problem. One friend said all I have to do is replace the bolt and I'm done. The other friend said I have to remove my intake manifold and clean then replace the gasket. I've looked (maybe not hard enough) but I cant seem to find an answer. Here are some pics of my intake manifold.