I'm not responsible of your device, doing this you're taking your own risk and responsibility.
1) You will need:
• A T4 Torx screwdriver
• Some lubricant (specific for precision instruments, not olive oil ;P)
• A plastic pry tool
• A little needle
• Some patience
2) First of all turn off the phone, remove the back cover and the SIM card.
3) Start to remove all screws.
4) Open the device using the plastic tool, or something like that (also fingernails).
5) Let's see where is located the vibration motor.
6) If you want to remove the battery, this is the right way, but it's not compulsory for our purpose.
7) Hey, it's a nice board for a 150 dollars phone!
8) Put a drop of lubricant on the needle, DON'T use the bottle directly on the motor.
9) Put the small drop of oil on the pivot of the motor (sorry for the pic quality).
10) Reassemble the phone and remember to put the buttons in the right direction.
11) Check if everything is ok. YAY!