My S1 Roadster had K&N fitted at about a year old. It was three years old when I bought it, and after a number of years, and maybe 18,000 miles, the Maf sensor was oiled up. I'd never oiled the filter, and nothing in the service records suggest it had been oiled. Now my Roadster runs a Ford Air filter and no noticeable difference.

I fitted a K&N on my Plus4 a couple of years ago to get a bit more air through, so I'll see how that one develops.

DaveW
'05 Red Roadster S1
'16 Yellow (Not the only) Narrow AR GDI Plus 4