You are correct that assessing condo fees and making special assessments for repairs to common areas are governed strictly by the condo documents, and absent going thru the amendment process set forth in the Master Deed, the board does not have the liberty to ignore the document. Assuming the MD does not create a separate equal division in the case of special assessments, they have to follow division by percentage interests.
To questioners from West Virginia & New York: Although I am licensed to practice in your state, I practice on a day-to-day basis in Massachusetts. I answer questions in your state in areas of the law in which I practice, and in which I feel comfortable trying to offer you assistance based on my knowledge of specific statutes in your state and/or general principles applicable in all states. It is always best, however, to work with attorneys and court personnel in your own area to deal with specific problems and factual situations.
While I agree with my colleague , answering your question requires review of your particular condo documents. The Master Deed may require individual unit owners who have exclusive use of a particular parking space to cover the entirety of the maintenance/repair cost for their space.