I hear you bru. I remember you have always had issues with that flat roof of yours. A flat roof is a fsckup.
Rubber the kak out of the whole thing and hope for the best.
A few posts back I felt the same way. Bought a 20L Duram Rubberflex only to find out the culprit was a known to me issue. The 2nd story gutter was totally blocked and the overflow went onto the balcony and the balcony drainage pipe has an issue that I need to attend to again and it was blocked as well.
So there I have it. R1800 bucks for fokkol.
And as luck may have it I had a friend over this afternoon that tuned me fok he has to go buy a bucket of rubberflex for his roof. So guess where my rubberflex is going.