Before I get into a trial and error experiment in an attempt to stop the gear oil leak coming from my tranny reverse switch, I was wondering if anyone has had (and solved) this problem (using X as a sealant?). Thanks in advance....

JB weld? no personal experience, and i await someone to say "NO!", but it worked on my BMW's oil pan when the PO hit a rock

From my experience, if fluid is leaking out of the reverse switch, the tranny is over-filled. Oil should be about 1/4" below the fill plug hole, which is about even with the reverse switch. I have even heard of some who fill the tranny thru the reverse switch when they can't break the plug free. In the meantime, maybe try some teflon tape (plumbers stuff) or maybe an O-ring on the switch.

It seems to be leaking through the switch itself not from the threads. The case was filled to the exact level and no more (I left the plug off until the level dropped to below the filler hole). I have about a dozen other switches but why put one in to find out it leaks too.

So what sealant stops gear oil (under a small amount of pressure)?

Yeah, I had that same issue on my Z. I replaced it with a new Nissan Reverse lamp Switch from Courtesy Nissan and it solved the problem on mine. I love when it's something simple