The Lucas you mentioned is a polyurea base. Generally these don't mix well but given your application I think you could just flood the joint out until you see whatever new color of grease you switched to.
I personally have mixed multiple types and never had a failure that I could say was caused by grease. We have fan motors that might get Polyrex EM one time, Mystik JT-6 red the next and probably some Schaeffer 221 in the mix too as well as hundreds of other bearings with who knows what pumped in them.