Front door Wooden Sill rotting

[psarinuk]

Hi,
Should I repair this door sill by removing the sill along with any the rotting wood under the door, then insert new timber underneath the door OR should I get a new door?
The door is Aluminium double glazed and feels quite strong compared to UPVC, so willing to hold on as long as possible?

P.S. I tried to repair the sill ~2 years ago using best quality wood fillers but it seems to be going bad again.

 

[blup]

You may be able to remove and replace the sill, if the door is in good condition and worth keeping.