spark plugs
 

I thought I'd change the plugs while I was changing the clutch. Someone has installed 4 trailing plugs!I've put close to 15k miles on it since I bought it. Has the engine been damaged?

Better than 4 leading plugs ;)

Yeah you're fine. Trailing are colder and might foul up easier, but plenty of people run 4 trailing with no problems. Just be careful leading are longer and if put in the trailing position could possibly cause problems.