the simplest thing to do is just buy an allen bolt. they are the kind that have the octagon looking hole on the top. it will be m6 thread and you dont want it longer than an inch. also buy a couple washers. all you need to tighten and loosen one is an allen key which is like 1$.
it will be made of stainless steel and will never break again. you might as well replace the other stud if you can get it out with the tools you have. needle nosed vice grips are the best. regular needle nose pliers will work if you're strong like ox.
if that doesnt work come back and we can teach ya tricks to get stubborn studs out.
the reasons i dont say replace it is studs come in certain lengths and threads. that will be hard to find locally unless you have moped friends.