Your post hit me very hard. My father was diagnosed with GBM in October 07 and my mother was the major caretaker. As with your dad, my parents had always ignored their health to degree feeling like living in the country was the cure to everything...healthy air and such.
My mom and I are very close and my dad and I were not at all. In January 08 after finishing his radiation treatments, he had a major seizure and was not able to walk again. I began the trip every weekend to my parent's home about 2 hours away to give my mom some relief. It's interesting how God uses situations to bring about change. I was doing it for mom...it turned in to doing it for dad. I will NEVER change the 4 months I had with him. God performed a miracle in my life...I now have this beautiful memory of the time spent with my dad that removed the 50 years of distance we had always had.
Caretaking is a tough journey. The strength comes . . . even on the days when you feel like you can't put one foot in front of the other. Whether you decide to walk this yourself or just be a support for your mom during this time, you will be amazed at how God can transform the feelings you have for your father.
You will be in my prayers. Hugs to you!
Cris