From my observation, Roland SC-55 MKI plastic front panel build quality is crap.
I have traded my Roland S-760 sampler (with ZIP drive + samples) for an SC-55 that is in pretty crappy shape (electronics are 100% healthy),

While trying the buttons i noticed some are stuck and respond badly to touch. When i opened the unit i first spent 30 minutes trying to figure out the damn while PUSH TO OPEN plastic thing. Luckily i didn't break it. So by the time i got to the screen part i noticed Roland used cheap glue, crappy screws into plastic and really bad button design. The button PCB seems completely operational.
Also the front volume knob, audio jack and MIDI IN is held by a SINGLE screw. Roland y u do dis?
I am thinking i can easily replace the box with a broken one.