Insights to Nedarim 21b addresses the difference between "Pesach" and "Charatah". The Rambam's opinion is explained in (c). Can you please read over the explanation and verify its clarity (specifically the last two paragraphs)? Also, the Rambam's opinion is explained much more in depth in Insights to Nedarim 78, but the explanation given here does not seem to appear there.
Yisroel Shaw, Har Nof
Is the second part of the question still a problem (after we worked on the first part)? Or please print the pertinent edited portion.