I would echo earlier responses - the Sumiko MMT is an excellent design and would certainly do a good job with a better cartridge than your Grado.
The cartridge hardly every wears out - it's the stylus that gets worn down and loses its shape. You find that it doesn't track as cleanly even when you're sure the geometry is spot on. Generally this would be after around 1000 hours of use.
The best way to check is by looking at it under a microscope.
It's possible that your stylus is covered in gunge - the Mr Clean Magic Eraser works well if you lower the stylus down on it and lift it again. Search the archive here for more info.
The cartridge hardly every wears out - it's the stylus that gets worn down and loses its shape. You find that it doesn't track as cleanly even when you're sure the geometry is spot on. Generally this would be after around 1000 hours of use.
The best way to check is by looking at it under a microscope.
It's possible that your stylus is covered in gunge - the Mr Clean Magic Eraser works well if you lower the stylus down on it and lift it again. Search the archive here for more info.