Injector Pump Oil
On the bottom of the injector pump case and the body of the governor are drain plugs.   Remove both of these and let the oil drain out.  Put the plugs back in.  On the rear of the governor there are two 10mm bolts, one above the other.  Remove the lower of the two bolts.   Remove (unscrew) the mushroom shaped breather from the top of the governer using a 13mm wrench.   Pour oil in until it runs out the check plug you removed.   Replace the check plug and breather.  Some pumps have an overflow on the bottom right hand corner of the pump (banjo fitting).  Some oil may drip from there at first.  Should check injector pump oil at least once per year.
Pictures and info provided by Scott Stokke of Northern Tractor.