I don't know much about spas, but I have a Sundance Sentry 505/506 spa. I guess it is either the 505 or 506 model. I am not sure which one though. It is probably 10 years old or so. It seems like the pump is going bad. The pump is very loud and does not seem to run smoothly. There is a small leak somewhere which could be from the pump. How much does it cost to replace a pump (labor and parts)?

Labor on installing a pump can be determined only by the local installer that you call to come do it, everyone has there own rates. If you would like to purchase the pump and replace it yourself then I would recommend calling 877-936-2223 and giving them the information off of your spa to find the right replacement. Also make sure that the leak you mentioned is actually coming from the pump, though the pump probably does need to be replaced it may not be the source of the leak and you would want o make sure that the leak is being taken care of also before more damage gets caused.