Thanks Tom, yeah that was my question as to whether an O2 would be permanently fouled by raw fuel present in the exhaust gases.
'Learn something new everyday' ...interested in reading the posts (thanks Jack) on raw fuel present displaying the lean condition, this solves some puzzles for me with setting higher fuel pressures and yet still seeing lean A/F and yet fouled wet plugs! Thank You. Looking forwards to now getting it right, and having 10 cylinders fire, and maybe saving some gas mileage!!
Thanks Kovacs for reply, my cats were history long ago!