CHCK does seem to be particularly unreliable but to be fair to the breed, our 92 in Scatsta seems to be fairing better. In terms of serviceability rate, a big factor can be spares availability. A minor unserviceability requiring a new bit that could be fitted in minutes, can turn into a day or two of AOG (or three or four if over a holiday period) if the part is not in our stores. Both manufacturers suffer from this problem and the operators are in part to blame because they do not want to hold stock of unneeded parts. The trick is in identifying in advance those parts that you will need!
HC