I have been fighting this problems for a couple of years. Keyboard still works great, but several most used letters wear off. I have tried different paint pens with no luck. Tried using nail polish and different clear tapes over with no luck. The best thing for me has been those tiny round color coding labels that are 1/4 inch. I clean the keys well with alcohol and then place the label on the key and write appropriate letter on it. They last about 2-3 weeks and then I replace them. It is a pain, but I am too cheap to buy a new keyboard when it works just fine otherwise. I wish the keyboard people would make them to last. I know there are those clear plastic keyboard covers available, but I cannot stand the feel of them and they slow me down too much. Have a great day!!