Looks like you may have a bleeder valve O-ring seal that might need replacing. Or you may just need to tighten the screws a little. Take a look at this thread on Renntech:
http://www.renntech.org/forums/index.php?showtopic=14754&hl=pressure+valve
I also don't really agree with Jaxonalden that it is normal to see condensation drops on top of the trunklid. That means some coolant is coming out somewhere (either the coolant cap or the bleeder valve), and it really shouldn't because it's supposed to be a closed system. I used to have a little condensation under my trunklid, and after I removed and retightened my coolant cap (real tight), the condensation never came back. I also checked my bleeder valve, and it was perfectly clean, so I knew there were no more leaks from that area.