I'm just throwing a few ideas round in my head at the moment.
What parts do you all need on a regular basis that are expensive/hard to get?
For example:
Everytime someone wants a clutch, that seems to be a question.
Many people seem to be talking about replacing engine mounts - I guess as they are 10 years old and starting to look a bit worse for wear!
Brakes are a bit awkward, I guess, as people like to research and choose their upgrade to suit their budget.
So? Any other ideas?