rpm delo Gold is really good mineral diesel engine oil, be sure to use a new oil filter and be sure to run the engine fully warmed up so the oil can stay clean.
For really good oil buy mobil1 diesel or Liqui Moly diesel 5W40.. It will scrub clean the engine nicely.
With mineral oils - 5000 kms is a good interval unless you drive in sandstorms, run the engine dead cold etc. etc.