Either one will do the job. Amel first stated to use 20-40 since it was common with the diesel engines and didn’t require an additional type of oil. But then, Amel stated filling with 90 oil during services in Martinique and France. This sparked a big discussion on the forum. The short answer is 90 SAE is best and 20-40 is 95% as good.
With best regards,
Sailing Vessel - Cream Puff - SM2K - #275
Currently cruising - Curacao
Just changed c-drive seals etc.