Bad PCI-E x16 Slot/ Posting problem

I had been having a particular posting problem for a while; after the PC had been shutdown for more than a few minutes, it would not post properly (no beep, no output to monitor; sometimes beep but freeze at splash), and it needed to be hard reset several times until it booted properly.

I had tried everything, and have finally determined that it is the first PCI-E x16 slot that is the problem. My board has two (system build at bottom), and when the card is seated in the second PCI-E x16 slot, there are no startup problems at all. Two different video cards have confirmed this problem. The reason I do not simply keep the card in the second slot is because the poor airflow (it's at the bottom of the case) causes my GPU to run about 9-10C hotter idling and 14C hotter under load, even with an 80mm intake fan blowing directly on it.

Anyway, I am curious whether or not the slot is most likely defective simply, or if there is anything else that might be causing it problems. I would RMA the board, but after having moved across the country I am having difficulty locating my UPC's/receipts. I would love to hear any ideas or suggestions!

My system: M2N32 SLI Deluxe Wireless (top blue slot [#1] is unstable one), ASUS EN8800GT 512MB, Sound Blaster Audigy SE, Seagate 300 GB SATA HDD, PC P&C 610W PSU, AMD Athlon 64 X2 5600+, ASUS 16x DVD, 2GB Crucial Ballistix PC2-6400 RAM, Centurion 5 case, Samsung Syncmaster 906BW