I pulled out my jack the other day just because I'd never bothered to look at it before. It was rusted on one end. I reached down into the cavity and there was 3 inches of water in there. It was slippery and stinky too, I 'bout barfed, grossed out. I can't tell where it came from, it's all sealed where I can see.
I sometimes use a touchless Laserwash, and when you slowly enter, it hits the underbody and wheels with high power spray. That's all I can figure. There may be a plastic plug to drain it. If it happens again, I'll either pry it out or punch a hole in the lowest part. Y'all may want to check your P5s. I don't know about sedans.

 

i think this has been discussed before, basically its your taillights housing that is leaking.... but if you have a nice subwoofer in your car you may have unintentionally loosened some seals in your trunk...

 

That stuff is normal and my guess is that its possible it could be factory, i noticed it one time after i was cleaning my car and had a undercoat put on, for me it was a purple pink color, sticky, about an inch but not touching the jack, but ya i am sure if you pull up your carpet in your trunk you might notice it on the other side or in any other cranny, i am betting its just to prevent rusting.

 

Switch from boxers to briefs - it helped me!

 

Naw, briefs are too constricting. They make my ******* sweat, and then I have to sneak the old pocket peel
Besides, I cleaned the rust with WD40 and coated it with 20 weight, and bailed out the scum. No mo problemo.