Often those rubber strips (extrusions) shrink in length over the years. I would simply fill that 1/4 inch gap with a small amount of LEXEL or similar (non-silicone). It is good you cleaned the window frame channel. When I happen to wash the Scamp
outside, I direct a stream of water from the garden hose into the weep holes to wash out any debris. They should drain freely. Then make sure to towel up any water I may have sprayed inside.