Only mention your medical condition in the research/personal statement if it is specifically relevant to your research interests, and you feel that your personal experience strengthens your ability to carry out research in your chosen area. (Example: you wish to do medical research about epileptics' sensory perceptions prior to a seizure, or auras; you might conceivably want to mention your personal experience with auras, if you think this will help convince a committee that they should assist you in doing such research. Although this is the best example I was able to come up with, it's still pretty lousy, in my opinion. There are plenty of people in the world who experience auras, but who aren't qualified to do graduate level research on auras! It's the person's academic qualifications, I think, that would be the most meaningful thing for a committee to look at.)
Under Section 504 regulations, pre-admission inquiries as to whether an applicant is handicapped are specifically barred.
If you are accepted, on your academic merits, the next step is to contact your institution's student disability office in order to document the disability and request accommodations if needed. The student disability office will work with you and your professors. No one will perceive you as whining. You will be perceived as someone who is a strong health advocate, and you will be admired for persevering in spite of adversity.
A person with a disability has as much right to an education as a non-disabled person. You are a person first, and a person with a medical condition that makes studying more challenging second.
Note that in Section 504, the definition of a “handicapped person” is not only a person with a mental or physical impairment which substantially limits one or more of his major life activities, but also anyone who either has a record of such an impairment in his past or is regarded as having such an impairment.
About the B+ average in your Masters and your perhaps reduced GRE performance.
What should have happened: as an undergrad, you work out a 504 plan with the Student Disability office at your school, with accommodations, including, for example, in the GRE, extra time, and rest breaks.
A helpful resource: A Layperson's Guide to Section 504
Some related, inspiring reading: A Short History of the 504 Sit-In