Hello & Welcome,
Sorry to hear of any issue you are having with your phones.
To help you with this issue, may I ask:
1) The FULL Model Number of the phone system you are working with? For a cordless system, that model should be printed on a sticker on the bottom or back of the main base unit and START with KX-TG.
I have a link to a video that is pretty good at explaining how to take one of these handsets apart & get it back together, which is usually the hardest part of this operation.
Click here --> https://www.youtube.com/watch?v=O4kwnaUaFMg
Please be CAREFUL/GENTLE when doing this job.
As for cleaning the keypad and surrounding "plastic", I usually remove the batteries from the handset, then use a bit of alcohol and either "drip & rub" the keys using a lint-free cloth OR I will "soak" the keypad for a few minutes, the push ALL the keys (especially the "sticky one") quite a bit - until the keys "loosen up"
Also, I have a link to Amazon where you can get a replacement handset - if that becomes needed. A replacement handset would have to be "registered" to the MAIN base unit before it would function correctly.
Click Here for listings --> http://amzn.to/29i0OsI
I hope this helps. Please let me know what you find or if you have any more questions.
Thanks, ***** *****