As I said in another thread, I am not really in this industry but .. have been doing alot of reading and have pretty good common sense.

Usually in a lease (at least here in California) there is a portion that says how much of the security deposit could be kept for "cleaning" and also has a small clause about "normal wear and tear"

In a financial point it may be better to settle outside, since you may be resposible for your legal fees.

Also check in the lease and local laws on how to use the deposit. Alot of places say the deposit CANNOT be used for the last months rent in ANY CASE.