My better half's 93 Berlina's rear window mould has been leaking water for a while now. The roof, (above the mould) has slight rust in it, causing the water to seep through to the interior.

I've tried all my options, none of them worked so it looks like the rust will have to be either cut out and new metal welded in, or at least a very good bog job. The rust itself is only very minimal, we're talking less than a few centimetres but big enough to mean the roof leaks and the window mould doesn't do its job properly.

My mate reckons it'll probably cost close to 600 to repair, what do you guys reckon?