[papajam]

Not being at all familiar with late model Spiders, I can't say it's this connector or that connection. But I'm sure someone else can.
But since both tail lights are affected, I'd look for something common to both. Like a multi-pin connector or a bunch of ground wires screwed to the body somewhere in the trunk. For the connectors, I use a run-of-the-mill electrical contact cleaner. Then use enough dielectric grease in the plug so some squishes out when assembled. The grease prevents moisture penetration virtually eliminating future corrosion. The ring terminals at the ground connections can be dressed with steel wool or sandpaper.