The buttons work by pressing a piece of conductive rubber-like material against two copper circuit board traces. This allows some electricity to flow between the two traces. I suspect in your case the traces have oxidized (think of how a shiny new penny turns brown after 10 years.) This oxidation interferes with the electrical flow. Pressing hard on the buttons spreads out the rubber-like material, causing its surface area in contact with the trace to increase. Increased surface area means lower resistance which means less interference with the electrical flow. If you're competent with a screw driver and very small screws, you could take your P1/P2 apart and clean the buttons' copper circuit pads. Something only slightly abrasive, such as a pencil eraser should do the trick. (Just make sure all eraser dust and bits have themselves been removed, before reassembling your Tamagotchi.) Note: neither I nor TamaTalk will be responsible for any damage you might do to your Tamagotchi should you decide to take it apart.
