In the mid 80's (showing my age now!) I taught Motor Vehicle Maintenance evening classes in Slough.It was intended as a basic maintenance course for idiots but I always ended up going more 'in depth'.Some of my (adult) pupils later became my customers.

One year, 6 months after the course ended one of my ex pupils rang:"Colin, my mini is using loads of oil, can you come and have a look please?"
"what do you call loads? , because they normally burn a bit I said"
"Two days ago I put a litre in , then yesterday a litre and just now another litre and its hardly moved on the dipstick"

"Blimey, that must be REALLY smokey or you must be leaving puddles of oil everywhere I said, don't drive it till I get there".

When I got there, she opened the bonnet and unscrewed the SU carb damper and said "look it hasn't moved on the dipstick!"

I think she must have been doing her knitting at the back of the class in that lesson!

Colin.