Aye.. you need to buy a 5ltr of oil... but keep yourself half a litre for top-ups.
When you fill it up.. stop filling it at 80% of the dipstick. My old Gerrard was filled to the "MAX" when I got it and I did find a lot of oil in the inlet manifold and pipes.. and the MAP sensor on the back of the inlet manifold was contaminated.
I dunno if the previous owner tended to over-fill it / once or whether the beast just has a high crankcase pressure.. but it's been happier with a tiny bit less oil than the "MAX" mark.
Ralf S.