Two solutions. Replacement rubber key pad membrane or re-apply conductive coating.
1) Call Sanyo and see if they have a replacement rubber membrane keypad for your model of telephone. (I replaced the keypad membrane on my Sanyo CLT-2430 cordless phone). In Canada, the Sanyo telephone number is: (905) 760-9944. Their web page is: sanyocanada.com.
2) A rubber keypad repair kit is available from MG Chemicals. Rubber Keypad Repair Kit 8339.
This kit is described on their web page: http://www.mgchemicals.com/products/8339.html
In Canada, this keypad repair kit is available from ElectroSonic. See a description of this kit at: http://www.e-sonic.com/acc/products.aspx?command=detail&partID=8339&partIDExt=281
In Canada, this keypad repair kit costs about $14.00.