Repotted two of these in March. Only one has forgiven me.

March isn't the problem, drainage usually is. If the pot has no hole at the bottom nothing else matters 😄

True.

how do you actually tell it's overwatering and not something else, is there a sign before the leaves go

Stem gets soft at the base first. Check before the leaves.

soft as in mushy or just bendy? mine feels bendy near the soil