I've recently had this issue with my 885, and since the remote was out of warranty I took it apart and after a little experimentation have now figured out how to repair faulty buttons. I've tried to describe the procedure I followed below.

You will need some clear sticky tape (I used some extra thick tape I had lying about - the thicker/stickier the better), a cotton bud, a craft knife, and a small cross-head screwdriver to undertake the repair (as well as some patience and a little time).

1. Remove the battery cover and battery, and take the back off the remote (two screws on the back - one at each end), you can then pull off the front of the remote to show the internals. Its quite stiff but does come away.

2. You can then detach the circuit board from the remote (2 screws - one on either side of the board). You will need to detach the cable from the top of the board to remove if completely from the casing. This is done by detaching the little plastic connector at the end of the cable attaching to the board.

3. Its then necessary to remove the LCD screen (you can't get to the internals of the buttons otherwise). On the back of the board there is a miniature ribbon cable that can be detached from the board (need to pull up on the plastic connector attaching it to the board and then slide the ribbon cable out). The LCD can then be un-clipped (a small clip on each corner) and removed from the board.

4. Then the plastic cover (with the holes in it for each button) needs to be peeled back from the top of circuit board. Its lightly stuck down but does come away if you pull carefully. When I did mine I only peeled it back about 80% of the way as the broken buttons on my control were in the middle of the control. This is attached to the bottom of the board, so be careful if you need to peel it back all the way.

5. You can then see that each button is in fact a tiny metal pad. These are all stuck to the circuit board by a clear plastic film which is glued to the board. All of the problems with the buttons on my control were caused by moisture getting into the remote which degraded the buttons(I think one of the kids may have spilt something on it?). The volume up button seems particularly prone to this as its at the edge of the remote where moisture can get in most easily, so a simple clean of the contacts on the board is all that was needed to get my remote up and working.

6. All of the buttons (one completely failed and another 4 or 5 which didn't work well) were repaired successfully by cutting the plastic film with a craft knife around the metal pads and peeling the film and buttons away from the board (if you can remove as much of the plastic film as you can its easier). You can then use a cotton bud to clean the contacts on the board and the underside of the metal pads (which first need to be peeled away from the plastic film). The metal pads can then be placed carefully back onto the board in the exact center of the contacts on the board (with the domed side upwards - the pads are shaped so that when pressed in the middle they make contact with the board so its important to get them the right way up). Be careful not to touch them with your fingers once cleaned. The clear tape can then be cut to size and used to stick the pad back onto the board.

7. Once all of the faulty buttons have been cleaned, the remote can be re-assembled. This is a straight reverse of the dis-assembly. Don't forget to re-connect the ribbon cable (simply slide it back in and press the connector back home to make it firm) and reconnect the cable to the casing back to the top of the board.

I managed to repair all of my buttons in less than an hour by following this procedure. This is a bit time consuming and rather scary given the level of dis-assembly / unsticking that is necessary, but not particularly difficult and resurrected a remote that I would otherwise have had to replace.

Good luck - I hope you have the same success that I did!