I always use Keyparts who give the choice of genuine parts or pattern parts where available. I use genuine parts as the additional cost of once a year is minimal in the whole scheme of things. I can understand those who run many hours a year and do multiple oil and filter changes using non genuine (like I did on my charter boat doing 4-500 hours a year), but for a private owner doing the typical 150 hours a year, the difference, including oil is less than £30 a year.
Another source is parts4engines who are Perkins specialists - the 2020 is a Perkins engine.
