Hello and thank you for your question.As you probably noticed when you took the Juno apart to clean it, there is a circuit board underneath the front panel. The buttons on the panel push down on switches that are soldered to the circuit board. These switches can fail for a number of reasons, but most often the metal contacts inside just get tarnished over time. Unfortunately the sealed nature of these switches means that they don't respond to cleaning attempts very well. They need to be replaced when they start to fail.Replacing the switches involves using a soldering iron to remove the old switches and replace them with new ones. If you are experienced at soldering it is fairly easy. But if you have never soldered before you should contact a local repair shop to do the work.You can order the necessary parts, or arrange for repair, through Roland online via their MyRoland page on their web site.
I hope I have satisfactorily answered your question. Please let me know if you need any more information or clarification on this issue.
Just as I feared. Thank you for your help.