I just did mine about a month ago and now I have a carrot so it's my back up.
Radio Shack Parts:
On-Off switch 275-1565 $2.08
Vibration motor 275-0107 $3.99
I also found a bag of 2 knobs that fit over that tiny sensitivity knob on the end and hold on with a set screw, just cant find the part number on that. I popped the speaker off the back cover and stuck it up the tube from the inside a little ways. Cut down on the noise. Took a rubber chair/table leg end that was 1/2 inch and put it on the end of the wand to cut down on wear. Hope this helps.
Do a search on Youtube and you'll find a bunch of help and numbers too. There's also a sticky at the top that deals with the HF Centech pin pointer.
The switch replacement is a must with these units. Mine stopped working the first hunt. Since then, I've removed the speaker, added a motor and ran a bead of silicone around the seams to keep debris out.
One other mod I'd highly suggest is adding a thermistor to the board. In extreme climates, the unit will false constantly. I tend to leave my gear in my trunk, and it will not function at all after being left in the heat, even on a mild day. I'll have to look up the part number, but I remember the component being under a dollar. Other than that, I've abused mine for the past few years, and it's held up.
One other mod I'd highly suggest is adding a thermistor to the board. In extreme climates, the unit will false constantly. I tend to leave my gear in my trunk, and it will not function at all after being left in the heat, even on a mild day. I'll have to look up the part number, but I remember the component being under a dollar.