Mine is always and I mean always difficult to get off.
To remove my RM2 from my Reo, I will give it one more turn right and then if I apply downward pressure, I can unscrew the base without the top cap coming along with.
I then grab my needle nose pliers and hold around the brass part, then I can just twist off the top cap easily. Sometimes I will just screw it on to an atty stand too.
Sometimes I can't get the top cap to spin without loosening the base, so I hold the bottom of the base with my thumb and eventually, ill get that top cap to budge if no juice anywhere.