Just after peoples thoughts. 
Changed my spark plugs today, bought the NGK Iridium ones from Awesome GTI.
Straight forward swap, noticed on the 1st pack I pulled had wierd rust type stuff on the end, pulled the spark plug out & that was the same. 
Ran out of time today but will pull the plug whilst the engine is running tomorrow. 
Wondered if anyone has experienced this & it's just the pack. 
The clean spark plug is what the other three looked like. 




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