What is the shelf life of the spice known as "sumac"?

I have kept a sealed jar of the stuff for about 2 or 3 years.
I opened it up today. It smells as wonderful as ever.
However, I noticed that moisture has condensed
on the upper side of the jar's top... obviously from the
ground sumac leaves themselves. There does not
seem to be any visible mould or spoilage, but I must
wonder what could be in the spice itself. Does anyone
have any experience with this? Is the sumac safe
to use?