tweake:

 

just keep in mind that the golden rule is all windows leak.

 

check the drainage path. not uncommon for people to incorrectly seal up the drainage path under the bottom of the window.

 

Aluminum windows are designed to leak, and the  the rubber seals around the edges usually have small gaps in the corners as they shrink over time so water has a clear path in.  So they have drainage holes drilled in them, and must have some drainage holes in the front of the frame .  Over time though these could get clogged up