manual which I have for Perkins
100 series engines including Perama
20,25,30 hp and dated up to 1994 lists:
quality - API spec CD or Mil Spec 2104C
Viscosity- any straight weight grade from 10 wt to 40 wt depending on ambient temp, as well as 15w/40 and 20w/50-- Note: 15w/40 has the widest temp range shown stretching from 14Deg.F to 122deg.F (-10C to 50C)
As CD is now an obsolete spec you will probably find oils readily available in CF or CJ ratings and with viscosities of 15 w/40. These will work
fine in your Perama 35.