JM,
If, as is probably the case, you can't purchase the special 4-pin spanner to fit, you can make one from a 12-point socket. If you have access to a mill, you can do it more quickly but you can do the whole job with a Dremel or other small grinder. Go to a discount or autoparts store and buy the cheapest standard or deep pattern 3/8" or 1/2" drive 12-point socket. The OD of the socket must fit inside the hole around the nut. The ID should be equal to or a little smaller than the distance across the nut between the bottoms of two opposite drive semi-circles.
Cut away the end of the socket leaving 4 pegs sticking out. Use the outline of the 12 points to achieve the 90 deg. intervals between each peg. Then grind the ID of the pegs to fit the profiles of the four indentations.
I've never had to do a 4-pin one but I have had to make several 2-pin ones by this method over the years.