What to do about leaking Aco drainage channel

[Postik]

I have an Aco drainage channel that runs the full width of mine and my neighbour's semi-detached garage. If the channel just caught water from the sloped driveway it might not be so bad, however it also catches rainwater from the garage roof which comes from a down-pipe on my side.

I noticed today after clearing leaves out of the channel that one of the joints has a gap and what appears to be a small cavity in the concrete underneath, and rain water is making its way down the gap instead of running the full length of the channel into a drain.

The channel itself is tarmaced in place so not an easy job to replace or to try and close the gap.

Any advice on what I can do to try and remedy this? Attached are a couple of photos.

Thanks

 

[foxhole]

Seal the gap .

 

[Postik]

Seal the gap .

Any recommended sealant I can get from Screwfix?

Also since there is a cavity underneath the gap I feel like I need to pack this out first. Would expanding foam work?