I haven't opened a Juno-D but I have opened a few others, Juno-106, 60, Juno-G, etc.
The Juno line seems to be assembled to come apart fairly simply. The Roland Samplers were a whole 'nother story.
Remember the old 106 and 60's? That was nice- a couple screws and the thing had a piano hinge on the back just opened up with plenty of room to see everything.
If you rely on the Juno-D and see yourself using it in the future (and can afford it) a replacement while you can get them wouldn't be a bad idea. You could dump all the settings from one to the other to have two of the same setups and be prepared for disaster.
When we played a lot in Chicago we used a couple W-30's this way. If one had a problem the other was always ready to run the show. We relied heavily on those boards for sounds, changing patches on guitar processors, other rack FX, etc. Having to play without one would have been a whole different show!
I still have that thing around here somewhere... along with a couple hundred floppies it accumulated. Oh yeah; there's still an extra floppy drive for it that should be with it too.. hmm.. time to get into the 'old keyboard closet' and see what else is in there I haven't thought about in a while.

BTW, I had the exact same symptom on the W-30 and dissassembled it to see what was causing the problem. It took a long time to get to the keyboard sensing pad, which I removed, looked at, wiped off and put back. When I got it all back together it worked fine..never did know for sure what caused it. I probably should have just shook it beforehand, but it was a pretty heavy board.

I do not work here, but the benefits are still awesome
Make your sound your own!