sliding window leaking between glass and gasket - fixable?

Something is keeping the water from getting to the weep holes. Those gaskets do not form a watertight seal; they just "mostly" keep water and general schmutz out of the track. At least on my windows, they're relatively easy to pull out and not too hard to put back in place; and I suspect if you did that you'd find there's a good bit of general debris all around underneath the gasket, and further cleaning it all out would make the window drain properly.