I and the rest of the Moderator staff offer our sincere condolences on Rambo's passing. I think most of us have experienced this loss, I know I have. My last parrot, Max, was fine one day, perfectly normal, and then he just .......... went away. No warning, no inclination of sickness, just gone.
I still feel horrible about losing him, with the same thoughts you have, about what could I have done better, different, smarter - anything. There is no point in beating yourself up. What makes me feel better is remembering all the fun stuff we did with him, his off little quirks, calls and mischiefs.
Also, you should know that I make a twice yearly donation to the Cornell University Vet program, directed to be used exclusively for parrot related studies and programs, in the name of Parrot Forums and I list each and every one of our feather babies on here who have crossed the rainbow bridge in the period. Rest assure that Rambo's name will be in the next donation.