Sadly in same position – upstairs balcony not waterproof and wrecked my ceiling paint. I got told the same thing, and from a quick google browse, I unfortunately thing they may be right. I believe if someone is egregiously negligent – example being given as leaving the bathroom tap on – you can make a claim which is then spread amongst all leaseholders (even though it is a claim against 1 person – weird). Otherwise, it is a case of claiming on your own insurance. Something I don’t fancy doing as I’ll lose my “no claims”. If you find out anything positive, please do report back!