420 of that era IMHO was one of the best engines Scania ever made in my humble, if looked after they were very reliable and i had terrific fuel figures that i have not been able to better (consistently around 15/20% better on fuel than 420 and 380 Volvo on the same work), they’d run happily all day long without once going over 1100 rpm if you drove them in manual…must stress i’m not an OD but i had one of these for many hundreds of thousands of trouble free miles as did others on the fleet, all were worked hard and heavy, tare alone was around 22 tons.
If it’s the three pedal opticruise box as was common at the time it might seem a bit odd at first but it proved totally reliable and very good to drive in MH mode, Manual mode in MH you get faster gearchanges than in normal M, left to its own devices in auto it’s a bit bleugh
Again not an OD, but I had a 2008 R480 drawbar 3 pedal opticruise for 6 years and it just kept going with no problems running at 44 tonne most of the time. Subsequent owner still using it, though on lighter duties. The only breakdown in all that time was a broken fan bearing. It was even happy going up Sutton Bank fully loaded, though only in manual!!