There are four areas that may be the cause of your problem.

The first area is the rubber bead that surrounds the glass and acts as a buffer between the glass and the sash or frame. You mentioned that you caulked this and that the leak persists.

The second area is faulty or non-existent flashing at window installation. This flashing, which may be metal or paper, is installed during the framing stage when the windows are installed. The only sure way to correct this problem is by removing the entire window, and surrounding material properly flanking it and then re-install it.

Caution: This should be done as a last resort, and only after all other methods of repair have been examined.

Improper frame assembly is the third possible cause for leaking windows. If the connections at the corners are not properly made and caulked at assembly, then this is sure to be a problem. Generally, a dab of clear silicon caulk will solve the problem.

Finally, clogged or non-existent weep holes will not allow water that builds up in the frame to escape. These mini-drains keep the bottom track from overflowing to the inside of the window. If these holes are dirty then a thorough scrubbing with a nylon brush is in order. If they don't exist, you may simply drill a few small holes at the exterior of the base track. Should you find that you are not able to make these repairs yourself, we recommend that you contact a glass company that specialize in window repair.