Transmission(?) Leak

Hello All, My '93 Chevy G20 Van 5.0, with an automatic transmission has developed a transmission leak. This vehichle is rarely used, and sits parked nose down on a very slight decline. It hasn't been started for a few weeks, but I noticed last night that a very recent puddle of fluid has been deposited on the driveway. A check revealed that the nose at the rear of the tranny is wet, which make me think seal. The weird part is that the drip is coming from the tranny's universal joint yoke at the driveshaft. I saw it drip and wondered why it would wick itself, uphill, to the universal. Although the nose(?) is obviously wet, it is not dripping. The only drip is at the universal joint. Common? How/why would this thing start to leak after sitting idle for so long? Is the seal the only concern here? Thanks.

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