If my lease mentions no time frame, is it by default month to month?

precisely.if your rental payments are current and you pay the last 30 days, sending a certified 30 day letter(return receipt) should be sufficient. leave the apt. tidy and you'll have no issues. you'll be needing his reference someday when you're renting elsewhere. if you treat him the way you'd like to be treated(weasel or not),life should be good.