With Norm there, quite likely it was low/out of oil. Ask 'em when they last did the oil change or checked the level, when you get the 'huh?' you'll know for sure. Although I'm sure you saw what oil (or remains rhereof) came out when you opened it.
Mowing on a steep slope a lot can also do it 'cos it won't throw the oil around properly, exacerbated by low/old oil further.
Even if the son was trying to prove 'red ones go faster' if Mummy hasn't been maintaining her equipment it's not entirely his fault.
I think best answer is Norm's and Mum's more likely to stump up the $$$ if you can get her to think it's partially her fault. You've got a good manner, Sean, I reckon you can probably pull it off. You can point out the importance of oil with the broken conrod (whoops that's my usual baseball bat diplomacy shining through again
)
