2003 Pontiac Montana Brake lights - base of bulbs melting

Yep. The socket base is a unit that holds all 4 bulbs on each side. I bought replacements for both sides from Rockauto last fall. That didn't help. I don't think it's a problem with the contact between the socket and the bulb. The don't see burning on the bulb from a sparking short. The bulbs just look melted.

I know some part of the cruise control draws electricity downstream from the bulbs. When the bulbs are both fried, then the cruise stops working. Could that be the problem? Would an measure of amperage downstream after the bulb indicate too much draw? Do you know of any way to troubleshoot something like that?

Mine is a 2003 model. Have you found any good way to systematically isolate the problem?
After the initial bulbs lasting what seemed like forever, each new set lasts a shorter and shorter time period. I had both brake lights out and was pulled over my police on April 5th. Replaced them that day and now my passenger side is out. I am down to them lasting about a month. It's ridiculous.
The plastic at base of bulb was melted. No other problems in electrical noted at this time.
Any suggestions because I am going to have to take it in and don't want to spend a fortune with them investigating and end up with a crazy huge bill.
Any help would be appreciated!
BTW the dealer is telling me to replace entire circuit board for each side. Approx $56.00 each.)