Brittle turtle shell

I have a LTC eastern box turtle who's had a brittle looking shell for quite sometime. I've tried daily soaks and increasing the humidity in her enclosure, neither of which have had any effect. I was wondering if this is just the way her shell looks or if theirs an underlying problem. She's lived with one other box turtle as long as I've had her and the other turtles shell hasn't appeared brittle or unnormal. Besides the brittle appearnce of the shell there's been no other problems with her health.

Aside from the light brown patches, the shell looks completely normal to me. It looks like at some time or another something happened to 'burn' the top layer of keratin just every so slightly. Too much sun? Too hot a light? A caustic shower? Who knows. But it's not harming her and it is really quite ok. If you'd like to get some lubrication onto the shell, I've used a light film of either olive oil or coconut oil, then polish it off real well with a soft, absorbent cloth.

Older boxie, & as Yvonne says, a fairly normal carapace. Not much sign of white growth rings, so a mature lady.

Ken