This is the switch that you need.
MHPS2266 Apem | Mouser
http://www.mouser.com/ds/2/26/MHPS_TACTS-369892.pdf
Be wary of the cheap switches that you see on eBay and Amazon. I tried some of those and they were non-latching, despite what the description said.
When you order the switches, buy several extras. They are real easy to damage when soldering or reassembling the unit.
When replacing the switch, there are several things that you need to be aware of:
1. To de-solder the old switch, you will need a low wattage iron and some de-soldering wick, both available at Radio Shack. A solder sucker is helpful as well.
2. I found it easier to cut the old switch base apart with a small pair of side-cutters and de-solder the pins one at a time.
3. Make sure to mount the replacement switch on the correct side of the board. I'll admit, I got in a hurry once and soldered it onto the wrong side

4. Pretty much plan to re-solder the wires in the 3-conductor cable going to the sensor. Two of these wires are solid magnet wire (red coating) that don't like to flex many times before breaking.
5. When putting the pointer back together, I used a piece of electrical tape and tightly taped the switch so that it was fully pressed down. Once reassembled I used a hobby knife to slice the tape away from the switch with it installed in the housing. Take your time pushing the board back into the housing in case something is not lining up. As you found out it takes just the slightest amount of force to break the switch.
While you have the board out of the housing, inspect the solder joints from the battery connections with a magnifier. These can get small cracks in them that can cause intermittent operation. Also you can use a small tool to slightly bend the battery contacts out so that they make a better connection (if that was a problem before)
I would not attempt this job unless you have some hands-on experience with soldering surface mount electronic components. I figured I'd post the above info to help out any others who have this same issue.