The cartridge guide is of utmost importance. Whereas the rotors themselves are more forgiving than a lot of people give them credit for, the guides will be the determining factor in the interchangeability game. It's certainly possible that someone along the way swapped it out - who knows? If all else has failed I would certainly try a different guide, can't hurt. All you need is a tiny drift punch to knock down the two little pins that hold it, and the skill to hit the pins dead nuts so as not to bugger the surrounding steel.....
