Rusty Roof Channels - is water getting in?

[Floss Regularly]

Hopefully the pics below are good enough to show a thin rusty gap/line running the length of my nearside roof channel. I have already searched on here and unless I misunderstand it looks like this part is more filler than bodywork, hence why it's a little spongy to the touch. Anyway, my main concern is that the 'rusy gap' means water is able to pour straight into the cab. Is that the case, or is there actual bodywork underneath still? I'm hoping that the 'gap' is a case of 15 year old filler contracting, rather than the actual welds splitting. I know I'll need to fix it, but if you could confirm that the rain we're getting at the moment ISN'T pouring into my cab, that would be rather super.

Temp fix: silicone grease
Summertime fix: follow the advice on here!

And while I'm here, water runs down the channels and UNDERNEATH the foamy rubber around the windscreen (last 2 pics). Is that right, or should the foam/rubber be firmly glued against the bodywork? Currently, it can depress it and pick at it with my fingers and the channel seems to want that to happen, so I'm hoping that's normal! My last car had the rubbers firmly glued to the frame.

 

[Old.Tony]

You are correct in assuming that the channel has metal underneath it (or the roof wouldn't be held up). In fact, there's a line of spot welds underneath the filler.

I had thought that the filler shrank here in Australia because we often have summer temperatures over 40C (104F) and I've got a pic somewhere with my car showing the outside temp at 49C (120F). I still remember how hard it was to just breathe the air that day! But it does seem that it's simply an age thing.

You can dig the filler out and (after cleaning the surface beneath and treating it for any remaining corrosion) refill the channel and repaint it.