Disklavier

I have a millennium edition DC3 Pro that has developed an issue with the key
sensor on a couple of keys on the high end of the keyboard.  The sensors
aren't completely out, but rather seem to have only a couple of levels of
resolution, so sometimes the keys don't send the midi output when struck,
and sometimes they do.  Even when they do, however, the output is very
"coarse" for those two keys. In all other respects the piano is operating
100% correctly.

My question is: Is this likely to be a bad sensor that will need to be
replaced, or is it possible that it is a dirty sensor that could somehow be
cleaned and not need replacing.  Before taking things apart and trying to
clean the keys at that level, I thought I'd find out if it is a losing
mission and I just need to call a technician and prepare to buy new sensors.

Phil