I had one of these cactus for many years and mine got long and leggy, furry... it never got as much sun as it would have in the wild. But it had its own weird charm for many years...see photo.
Eventually it got soft/rotted and died off.
I think you need to be careful about watering too much. Remember it stores water inside. Personally, I would water it thoroughly once every two weeks, not weekly as you have been doing. Once these cacti reach internal water saturation, they can more easily rot. I don't know if your 'chuck' is due to rot, but it's a wound and as such is now vulnerable to rot. I believe the white surface is just scarring over.