You can be surprised what can happen during a prolonged rain, even if it is just drizzling all night, hosing can escalate a bit, but nor always, as slowly seeping water can take hours, hence why hosing doesn't always reveal slow leaks. I would just seal the window as best as you can , no need to take it out, since in a few years time you might be going for new windows by the looks of those windows, (no disrespect) just bash loads of silicone.
I have just been to my rented house in Harlow doing similar patching up and siliconed a deflector strip to stop rain water overflowing the gutter which tends to water fall from just where my window is, looked at the gutter itself, it is in a perfect line, sloping towards left, where the down pipe is, so my gutters are not sagging, nor any brackets missing, and seems like brackets every 1 to 1.5 meters apart, so either clear it every bloomin 6 months or face water fall.
With this I hope my living room lintol wpuld stay dry from now on.
I have just been to my rented house in Harlow doing similar patching up and siliconed a deflector strip to stop rain water overflowing the gutter which tends to water fall from just where my window is, looked at the gutter itself, it is in a perfect line, sloping towards left, where the down pipe is, so my gutters are not sagging, nor any brackets missing, and seems like brackets every 1 to 1.5 meters apart, so either clear it every bloomin 6 months or face water fall.
With this I hope my living room lintol wpuld stay dry from now on.