Mammillaria carrettii

I just wanted to ask if this is a particularly difficult species to grow when it gets older? I have several plant sof this species, and they have all flowered well this year. The biggest, which had 5 heads appears to have rotted, literally within the last 7 days, which is when I watered all of my plants. The othe rcarrettii are fine, but this one decided it's time was up. The soil wasalmost dry when I tipped it out, my usual mixture which drains well, so I'm a bit confused.
Very annoying as it was a very nice plant.

I have (had) 5 multiheaded plants of M. carrettii, 3 of them are 22 years old and 2 of them are 16 years old. One of the oldest and one of the younger ones have rotted in the last few years. I did not do anything to save the oldest plant, it just happened that one head (on the edge) survived and is doing well again. Beside this healthy head there is a bunch of dead and dried-up heads. I did try to save the younger rotting plant by cutting away the dead heads, but I do not yet know if the two remaining heads will survive.
The 3 other plants are perfect.
Apparently this species can rot rather unexpectedly, but if you are in time you might be able to save the unaffected heads.

Wolter.

Thanks for the information, Wolter. Quite obviously I wasn't in time!