Without exception? I wonder what Mahabharata edition you've read. Yudishthir? Arjuna? Bhishma? Flawed?
Do you remember how the Mahabharata ends? The pandavas climb the ? (can't remember the name) mountain, and each one dies in turn. Yudhistra asks why, and a litany of crimes and misdeeds is read out. Finally, it is Yudhistra and a dog alone, and Yudhistra also dies. His biggest crime - gambling. Only the dog (Vishnu, if I remember correctly) manages to reach the top. They all ultimately ascend to 'heaven' but not before paying their dues. All were flawed.
The beauty of Mahabharata, apart from the prose, is in fact the fallibility of its characters. The foibles were created so that the common man/woman can identify with the characters, and learn lessons on how to overcome their weaknesses.