The chimney has a faux stone veneer on it that is crumbling I guess because it was never sealed properly. There are also cracks in some areas of the mortar as you can see in these pictures. What do you recommend to fix these?
These areas are not visible from the ground, so I do not care about appearances on it, I just want to fix it properly (no I'm not going to replace all of the chimney with new veneer). Thanks! Image links follow:
I see what looks like water intrusion due to an inappropriate tarred cap.
Remove the tar, remove all the damaged mortar and stone and rebuild it. Put a proper cap on the chimney or you'll be doing this again in a few years.