When i first bought my M600 it had been sitting for 3 years, i checked the oil which looked clear/red like it should so i ran it for a month or so, it ran fine. i was given 50 litres of Mobil DTE 25 Hydraulic fluid and when i drained the original oil it came out like chocolate milk!!! With the new oil it ran fine as well, what im saying is it doesnt seem to matter what type of oil is in it as long as it is of good quality.