As Bert has said, might be fun. As a parts distributor for over 40 years at Hughes Auto Parts and Oil Co., Inc. we supplied 12 sizes of grease zerks. Some are press type.
There are 1/4" 20 tpi which are the more usually found on most equipment across the board. However, another very popular size is the 1/8 NPT pipe thread size. I haven't seen any on the Hustlers round these here parts.
If the bulb is broken off of your zerk, you may be able to use a number 1 ease out to remove the 1/4"-20 zerk or a number 2 ease out for the 1/8 npt zerk.
If it is a push in, all I can say is: "have fun". lol
You'll get it and to get it, just begin and it will all be over very quickly. Well, probably not, however, lets be positive.
Good luck,
Max