As an update for those who are curious Diesel had two large tumors, one on his heart, and one on his spleen. One of them ruptured (though they could'nt tell which one due to the large amount of blood internally) which caused him to bleed out rapidly. So it is good to know that he didn't suffer, and that it is not a genetic problem.
Thanks again for the overwhelming support. It's good to have the MOA family.