Recently my croll was getting to the stage where it was just as good going down on some rope as going up, obviously the time for a new one although the wear to the cam was nothing like as bad as I had seen in the past, probably not doing so much these days in very muddy conditions.
 
what was concerning was that on comparing the old with the new, the metal below the bottom attachment hole (the critical one) had been reduced by about a half. This was not obvious without comparing it to a new one as the wear was fairly even round the bottom half of the hole.

I found the same thing with mine: the bottom hole seems to wear very quickly when compared to an older model Croll. But after buying my current Croll I have started using a Pantin. Do you use a Pantin? I wonder of the positioning is different when using a Pantin causing more wear on the bottom hole on the Croll?

I believe that, though I am willing to be corrected, that the alloy from which the Croll is made, is now - softer and more corrosion resistant than it used
to be.

What's the main harness attachment - steel or alloy, and is it a D or delta maillon, or one of the D or rounded-triangle krab-like things?

My wife had an interesting experience with a worn Croll. I was at the bottom of Aquamole watchung her descend, and when she reached the foot of the pitch she stumbled and fell, and the rope (9 mm) somehow caught in the bottom attachment hole of her Croll. To our utter astonishment, the circumference of the hole had been worn to such an extent that it was almost razor sharp ? and it chopped neatly through the sheath of the rope, all the way to the core. As it was near the end of the rope, it wasn't a big deal ? but she replaced it PDQ.

The last time I had to replace one the hole was pear-shaped, so the wear was obvious