my mate is as ham fisted as they come(once he managed to bend an m14 bolt on a Passat suspension mount changing the shocks with hand tools) and always buys german diesels and changes his glow plugs and even hes never managed to break one. ill give it a go myself ( obviously ive now tempted fate and ill break all 6)
eurocarparts has got a 35% off weekend sale so ill buy the most expensive option of ngk plugs.