Just saw your thread. I too struggled, and still do with masturbation. Like yours, my fight has been mostly 25 years of losing. Until now. I joined GYE, and started the 90 day challenge. I lasted 18 days, started again, lasted 18 days, and then started again. I was quite surprised when I kept myself clean for 194 days!!! My previous best had been 34.5 days. I am no again on the 90 day chart, and today is 30 days clean. Some points that I picked up on the way:
1) I am not as bad a guy as I thought I was. If I was able to keep myself clean on Shabosim. that meant that my souls is not dead to Kedusha. [If you managed to keep clean for Yom Kippur, that means the same for you!!!]
2) The biggest proof to myself that I am still in the fight was signing up to the GYE site. I found that even after 25 years of defeat, I still wanted to win. I still had that dream of one day maybe being clean. I wasn't sure that I could still fight, but at some level I still wanted to. [The very fact that you joined this site indicates the same. Your soul is NOT rotten to the core as you suggest. You did sign up to the site, after all]
3) I too had seen that Chazal, the more we satiate it, the more it hungers. It took a while, but I have seen it with my own eyes, and felt it with my own body. They are right!!! It seems the hardest at first, but the fight does get easier as time passes. [I fell because I let my guard down, and borrowed a friend's unfiltered computer. Even though there was a real need for me to have it, I overestimated myself, and I fell after around a week.]
4) This will be a long struggle. It won't necessarily be easy. But, it is a struggle that I can win. I kept clean for 194 days, I know that I can do that again. At first the number was much smaller, If I kept clean for 30 days, I can keep clean for 31 days. Then 32, then 33, etc.
5) I davened a lot, begging Hashem to give me the strength to keep myself clean, and to not overly tempt me. Many times, things just seemed to work out for me. After seeing Hashem's hand I things, I started to have an easier time with things. [I still fell anyway though]
All the best to you in your struggle! This is a hard, but ultimately winnable, fight!