The buttons in this x0xb0x had been worn out over the years. I replaced them with Omron B3W-4050 buttons. These buttons are a bit pricey (compared to No Name chinese ones) but they are sealed so dust and grime will not get into the buttons. Apparently the dirt is the main reason for the buttons going bad. The Omron buttons are the buttons recommended by Robin Whittle (of Roland TB-303 Devil Fish Mod fame) for replacement in the TB-303:
The cross cut mod used her is his idea AFAIK, but it works fine for the x0xb0x also. It is a bit harder to get the caps on, but it is doable; just be careful! It is a good idea to order a few extra buttons as you might break the stem while modifying it. Be careful and take it slow!