Sanyo EXCD-1000 Car CD / Cassette Player

My boyfriend bought and then installed this unit into my 1997 Nissan Sentra about a year ago. I've had some problems with it. For what he paid, it should work flawlessly. While having a CD and Cassette player in a single din unit is great, the face plate doesn't appear to be holding up to wear and tear very well, it seems a little loose. I've also noticed, during the last few months, the buttons don't work all of the time. This includes the power button, which sometimes changes the radio station rather than turning the unit off. Sometimes it takes several attempts to get the unit to shut off. The radio station preset buttons don't always work right away either, sometimes it takes several tries to get it to the station I want. There's also been a few times when the unit wouldn't turn on at all. During these times, my boyfriend and I looked high and low for the problem but usually came up with nothing. After we tried all different types of things, it would just turn on all by itself. My theory is that the bulky wires in the back get jolted around causing a loose connection. It's a pain to check all of the wiring, the amp connections, the ground wiring, etc. and still not have an answer. I'm aware that this could be an installation issue so I'm including this problem in hopes that someone else may have a problem like this with the model. Then I can confirm that it may be the unit.