Large Beech Tree Branch Split

[Billhook]

The other morning there was an awful noise as this huge branch split from the main trunk.  No wind at all, the cracking a groaning sounded like a firework display 

Anyway it is one of half a dozen that stand on the garden boundary and they are very fine trees and healthy and we want to do our best to keep them.  
The question is how best to stop water entering the split and rot the trunk.  I have used Arbrex successfully in smaller area but this would need a large amount.  Are there any other mixes that I could make that would not cost too much to fill the split?

I tried to push the remains of the limb into the main trunk with the telehandler boom to make the hole smaller, but it would not move even an inch and the telehandler has quite a lot of pushing power.  Must be reaction wood  

[Stubby]

Summer limb drop . Beach are prone to it I have found . Dunnow how best to protect the wound . Sorry . 

Edited Thursday at 17:34 by Stubby

[Tree monkey 1682]

It knackered, arbrex is an out  of date practise, if the trees no where property, leave as is ...

 Start planting a younger crop in front of the mature trees to take over if they fail.

[kram]

The split is past saving. The subsequent photos show soil/rot/fungus/included bark in the split, so its unlikely to callous up nicely whatever you do - it is destined to be a rot pocket/habitat.

[Billhook]

Thanks for those answers, I think I already knew that it was too far gone, anyway it will still probably outlast me, so next generations problem!