Perhaps some photos will help illustrate.
Normal behavior for E. resinifera is for older parts of stems to turn brown. Typically this is covered up by new branching as the plants age and the mound expands. In my experience it starts on the side that faces the afternoon sun and spreads around the plant. Nothing I would ever have the slightest concern about. Life in day-long sun is not that easy but these plants are extremely durable, and as long as they keep growing, the brown parts are covered up by green parts. Does that make sense?
On the first plant you can see the transition happening. The plant was mostly a long main stem with a few side branches when it went into the ground. The main stem is where the browning started. Almost all the branches from the bottom grew after it went into the ground about six years ago. These plants transform into monsters when they leave container life, given enough time.
On the second plant (which has been in the ground for longer and is a second clone) there are also brown parts like that, but they are hidden below new growth and I'm unable to climb up and get the perfect shot. There are some scary plants growing back there.
