I have been experiencing some moisture in my attic this year and would
like to get some advice on how to solve the problem.

What's in my attic:
- The attic has a continuos ridge vent with continuos soffet vent along
both eaves. The vents seem to be working and there is no insulation
blocking the soffet vents.
- The attic floor is well insulated with R30 insulation w/ an attach
vapor barrier facing the attic floor.
- My drop-down attic stairs has a battic door w/ insulation so there
shouldn't be any heat leak though the opening.
- The bathroom fan is vented through the soffet vent and no air is
escaping in the attic
- There is a gas hot air furnace in the attic which had some leaking
duct work. The leaks have been fixed and some additional insulation has
be added to the ducts.

I thought by fixing the leaks in the ducts, my problem would be solved,
but the North side of the roof still has some moisture. It is a two
story house located in eastern MA. The house does not have a lot of
humidity (usually around 30 - 45%). and the attic is definitely cold.
It has been a rather damp winter in the Northeast, maybe that has
something to do with the problem.

The only options that I can think of a

1. Add an additional vent where the furnace is located just in case
there is some small heat leaks that I missed. (If I do this, I'm
worried that this would affect the airflow for the ridge vent)
2. Install an Attic Fan w/ an Adjustable Thermostat and Humidistat with
the idea that the humidistat would detect moisture build and vent it
out. Any suggestions on what the humidistat should be set at (I'm
thinking 45 - 55%)

Please let me know if anyone has any suggestions on something else to
check in the attic, or what you think of my options and which one would
work the best.

thanks in advance