Ah... I understand now. I've never had this problem, so its just guessing. Well.. firstly, that bolt that broke... No. I'm pretty sure it's one with the whole arm. They are welded studs. I would think your options are:

In order of desirablility; least to first.

A) cut off the rest of the remaining stud and drill a hole where the stud used to be, and use a normal, removable bolt with a nut on the back.

B) Cut off and drill a hole where the stud used to be, and have a new bolt welded in its place. I woudn't think it need be oversized...

C) Replace the whole arm. A used one should be fine... perhaps someone here has one they could spare? If I did, I'd send it, but I don't think I've got any... Where are you located?

$60 for a replacement part.... I assume that used? If that's the price for a new one, that seems a real good buy. But used... I'd think you should be able to find one for less... But I'd also think you could fix the probem still using your old part for least expensive...

--
-Matt I ♥ my ♂