someone had cooked it through excessive leaning
At the risk of starting another thread on this... "excessive" leaning is a danger only at high power settings e.g. 75% or higher, specifically ones which result in high CHTs (perhaps 500F or so).
Excessive leaning alone just gives you a rough engine and a loss of power. No damage is caused.
During taxi, maximum possible leaning is the best thing - keeps the plugs clean.