Some red window problems may relate to other light paths between the window and the emulsion -- reflections behind the pressure plate or the like. A while back I tested my Perkeo II with full afternoon sun from different angles, 15 minutes on each test with the window slider open and could not see any visible effect with 400 film (TMax 400). So I don't worry too much about it. But I readily admit there could be differences between cameras as well as backing paper, so it is probably best practice to avoid unnecessary exposure.