Jack Johnson this "When I tap the volume dial,lean it against something, or just fidget with it , the sound comes back" sounds like a bad potentiometer. It may be gummed up, same with your cassette drive. Time to tear it apart and clean it all with some 90%+ isopropyl alcohol. Check the pinch roller, playback spring and drivebelt on your cassette player. Use [https://www.youtube.com/watch?v=WGXhaNY7SWo|this video] and an excellent refurb of Teddy Ruxpin. It's a series of 4 and goes over all the details [https://www.youtube.com/watch?v=92l128TM-7s|start here] for that. If unsure post some pictures of what you get with your question. Use this guide [guide|21499] for that. It will allow us to see what you see.