Hi Ira. The short answer is no, it is not true. The percentage will vary from building to building. Check this before you sign any contract.
Condo common charges (you referred to as maintenance) are not deductable. Unlike a Coop that includes the property tax portion in it's monthly charge, you get a separate statement for property tax when you own a Condo. Your common charges go to the upkeep of the building and many other things like liability insurance, snow and garbage removal, doorman, etc. As such, no deduction.