Isuzu d-max

I bought a brand new 250 x-rider double cab in 2020. Took it for its first service in December 2021. The vehicle always stand in a garage or under a car port. That weekend we went to Delmas, it was raining, it stood outside in the rain for two days. We drove back the Sunday and discovered that there's a leak inside the cabin, somewhere by the back window. The back brake light wasn't working,thought it might be there. I took the vehicle back the next week, they said that they couldn't find any leak into the vehicle. Now 10/03/2022 , we are on holiday. Drove 05/03/2022 to Durban and got heavy rain before the Drakensberg. We had rain yesterday 09/03/2022 in Ballito and the bakkie started leaking into the cabbin at the same place.