On 3394 (low bow tank WAPB design)I repaired leaks where the inner planking to the keel appeared to have gaps, simply by stripping back the paint and letting West ooze in, and then filling with West/Microballoons.

I note from the rules 'In boats of wood,
plywood or closed cell structural foam construction any part of the hull
surface finish (external or internal) may be reinforced by layers of woven
or non-woven glass-fibre.'.

Do you think I should glass the inner plank to the keel? Would that add anything and reduce the chance of the cracks opening up again?

Is this sort of leak common?

I've never seen the garboards come away from the keel like that!

The problem with glassing is if you don't get it 100% right water will get in and the wood will go rotten.

If it's not opened up again i'd be inclined to not worry!