Thanks a lot for your reply. I will have the mechanic look into the half shafts also if the new driveshaft doesn't totally fix the vibration.
You are right about problems caused by the car sitting too long. I recently started to use it more frequently, at least twice a week for a minimun trip of 20 miles, because the weirdest things kept breaking from lack of use. Now the more I use it the better it seems to perform.