This euphorbia is at least ten years old, and to my knowledge has never been repotted. I recently noticed it has white (sap?) spots all over it, save for the very tips of the new growth. It also has what appears to be some corking at the base, and quite a bit of scarring (round brown spots near bottom, and more slash-like holes as if being eaten away at). Some other facts:

- I have moved house several times with this plant and so its own spines would have penetrated it at some points, but some wounds look much newer

- I had it in a corner that likely had poor airflow

- I’ve recently paid much more attention to my houseplants as a hobby, and had some tropical plants nearby for which I had a humidifier going and I’d mist them

- the previous owner had some stones covering the top of the soil

- I was likely overwatering, although I was using a water meter and only watering when it read the soil was dry, but this was at least weekly

- I took some cuttings from this plant a few months ago (no sign of issues at that time that I noticed) and they show some similar signs as well as mildew (?) at the base

so far I have removed the stones, planted plant in an area with more light, stopped watering it, and tried removing the white spots with alcohol (at first thought it was scale) which didn’t really help, then sprayed with soap/water which seemed to make it worse (more white spots).

Please help! I want to save him if possible!!