Simon, Bad shame, had 4 engines go teh same way myself.
2 off them due to me learning to map and failing miserably

At £2000 a time to rebuild them properly it does hurt


FYI,

Dont forget lambda AFR is an average of ALL cylinders.
If one leans slightly for what ever reason, it is unlikely you will notice it in
time to save it !.

(Assuming AFR was the problem)

As most cossie engines are tuned to the limit during mapping it doesnt
take much to kill them depending on how much "comfort zone" a tuner
gives you but even then, when a minor fault or change occurs it will still
go bang in a few seconds.

Lock the garage for a few days, go out, get pissed, then rebuild it