I have a leak down my A pillar, not every time it rains but it takes time to build enough water to leak out.

 

Do you have a sunroof? Check the drains.

 

Yes I have a sunroof, what is the best way of snaking out the drains.

 

My sunroof drains got plugged with debris from trees I park under. I used a blower tip attached to the air-compressor hose. Opened the sunroof, stood up through the sunroof so I could see what I was doing and blew all the crap out of there. Pay extra attention in the corners, where the drains attach.