Waterproofing window sill with too little incline

[Bruce]

Our BCO is not happy with the incline of our window sill and say it might lead to water ingress. They alluded that the sill should not need redoing but they were not allowed to tell us how. So I'm after any ideas that we can use/submit on how to retrofit a simple solution to this problem. I'm thinking maybe suggesting something like the below pictured diverter but wanted to see if someone else has done something clever before me? We have had this window like this since August, without any selaent under it (life got in the way) and it has never leaked.

[MikeGrahamT21]

Something like this would be ideal, cut to the relevant dimensions and put under the existing sill

 

https://ewistore.co.uk/shop/external-wall-insulation/over-sill-2-5m-100mm-depth/