Are the streaks water damage? If they are dark shadows it may just be dust that tends to favorably accumulate on cold surfaces. This typically occurs at the wall studs because they conduct heat away faster than the insulated space between the studs. Very common if you burn candles or have a leaky gas furnace (bad) but can occur just from dust.
But if it is water streaks then it might very well be a flashing issue rather than a bad window. The flashing can be redone properly with the existing window so no need to buy a new one.
But if it is water streaks then it might very well be a flashing issue rather than a bad window. The flashing can be redone properly with the existing window so no need to buy a new one.