I posted the MH 600/700 manuals (applicable to the round head machines). The 800 machine looks very similar (the lube chart near the end says it is applicable to the MH 800A/B machines . There is a list of suitable oil for the main gear in the manuals (none of which I could find a cross reference for). I tried to sort through the Engler ° @ 50C - it hurt my head.
The main gear uses heavy straight cut gears (nothing special). I went with a Shell Tellus 68 (it is similar in weight to a 20W crank case oil). Most any hydraulic/gear rated oil (not too light), non-detergent, non-EP - just regular rust & oxidation inhibitors and you'll be fine