Sticky keys on Concert 3500. How to get in?

[twk]

Hi, a couple of the keys of my Concert 3500 have become sticky and aren't returning properly. I'm trying to work out how to open the case so I can attempt to clean them. Does anyone have experience of doing so?

It appears that the top of keyboard case is hinged but I've not worked out which screws to remove to allow me to get in.

[Marc7]

Same here, I have one key (the fourth D#/Eb) which is stuck and it ruins the whole experience as I have to to pull it back every time. Is there a workaround to fix this without completely dismantling a 70 pound keyboard on my own?
Cheers!