First need to pin down exactly where the water is coming in. Can do this by spraying water on the window with a garden hose while a second person carefully observes from inside. Possibilities are:
- Between the outer window frame and
fiberglass body. If this is the case, remove the entire window, re-seal with a thick layer (or double layer) of butyl tape and re-install.
- Through factory seams in the outer frame. Use a marine grade sealant or epoxy to seal seams.
- Between the sliding and/or fixed sash and the outer frame. If water is slowly rising in the bottom track, make sure the weep holes are not plugged up. Also look for gaps in, or missing rubber/plastic seals.
- Around edges of glass pane(s). This requires removing and re-sealing glass pane(s).