I have never had a laptop key button stay repaired for long. If you want to use the built in keyboard I'd suggest that you replace it. Amazon has them forsale new and used ones.
http://www.amazon.com/Eathtek-Acer-Aspire-ZA5-751H/dp/B008X09QC2
Another option I can suggest is that you get either a USB wireless keyboard and just not use the onboard keyboard. eBay has a nice one for $6.99 shipped (sold through Best Buy)
http://www.ebay.com/itm/Insignia-Wireless-Keyboard-Black-/321877278023?hash=item4af1617d47:g:gWQAAOSw0HVWB3~W