Well here is the response I got.
================================================================
"The MCD-50 (spa, 50 mg/hr) and 5-PA0213 (pool, 250 mg/hr) are different ozone cells. The swimming pool ozone cell is much larger is size, compared to the smaller MCD-50 cell.
The CDX-24R is not designed to be serviceable. When the ozone cell eventually wears out, the entire system should be replaced. I would recommend our next-generation SpaEclipse as a replacement."
=================================================================
I already knew the Sunzone CD wasn't meant to be serviceable. But inside, it's still just a fuse, transformer, power supply, and cell. I would think a replacement kit would work, but he didn't really specify. I did not realize that the ozonator for the EC series was for pool size; so I did learn something.