How is externally look like? Have to see outside. Sometime water slip in from the aluminium, rubber and also from the base like "halcyon27" mentioned the base not angle properly.

If the wall-aluminium frame already properly seal, next possible is the rubber seal or the aluminum L join, and to proper apply silicon sealer have to remove the old sealer before apply. Is better to have one single piece rubber.

If on top of the glass have anymore space (wall), maybe can consider put a 2-3ft awning