Glad to hear you sorted it and got to RR aye. Shame I didn't get to meet you though! But hey we're just down the road from each other so I'm sure we can sort something out another time
If you think about a fat plug thread made of steel being overtightentened into a soft aluminium housing it's easy to strip the aluminium away.
Then it's a 'pop out' job when the combustion pressure builds up.