Since it says to use shell, you might look at the shell Spirax i believe its called. if you dont want too i've used this (https://www.amazon.com/Lucas-LUC10043-Oil-80W-90-Heavy/dp/B0007ZFTOA/ref=pd_lpo_sbs_263_t_0?_encoding=UTF8&psc=1&refRID=69CEG4WFZ1W1FVE98EPC )
in my Mule for several changes, no problems at all.
EDIT: Or at least make sure its Low Foam oil