Why soft?
If the core is wet then I would not recommend drilling and injecting. If the core is dry then that will work if you don't mind the cosmetic blemish. By the way, after you have injected epoxy there will be a sag in each hole after the epoxy drys. Use A colored gel coat to fix or Marinetex. Coloring the epoxy doesn't work since it eventually yellows. First hand experience. It is not that hard to cut away that much deck. Can usually be done with a circular saw set very low. Replacing the coring, glassing etc is not all that difficult. Try and not to cut on the non-skid and you can get a pretty good repair. Of course you need to find the leak that started the whole problem in the first place. If the boat is in otherwise good condition and the price reflects the problem it may be a good deal. An older boat is going to have some issues so if it is 10 years or older I would take that into consideration. As advised in an earlier post, check with your surveyor. You may be able to get the whole deck painted if you work it right. Good luck.
