I clean my machines with the vacuum attachment, a drop of oil on the wick. Take out bobbin case and also clean the tension disk, use car wax on the bed of the machine to deter scratches and help with FMQ. I would never take in a machine for a costly cleaning if there was not something wrong mecahnically. I have computerized machines that are 30 years old and have never been to the shop. I have a family of Janomes that have never had problems. "if it ain't broke, don't fix it"......Care for your machine, clean it routinely and no costly trips to the shop. If it stops running, is out of time, or a feature is truly broken (thread cutter), then take it in to have the part replaced. If it isn't stitching properly, it is most likely user error....threaded wrong, thread out of take up lever, tension needs adjustment or bad needle. Why would you spend all that money when there is nothing wrong with your machine? Save the cash for more fabric! Yeah!
D in TX