I use a 5/16" socket head capscrew turned down to 1/4" in a drill press leaving some threads just under the head. Tap one side of the coupler hole and no more beating spirol pins. Dave Kamp has a site that outlines the procedure.

spiral pin
 

where is the best place to buy spiral pins for the rear coupler on my 126

McMaster Carr is where I bought my last ones.

I actually asked my local case IH dealer to make up a kit of various sizes for a decent price....probably 30-40 in there....or mcmaster

I was mowing a year or two ago and suddenly it quit going forward (hydro.) I moved the handle and nada. Experience told me it was the pin in the driveshaft. Sure enough....crazy thing doesn't like to move unless the driveshaft is going. Glad you got yours fixed.

Sometimes they don't break, somtimes they just wiggle enough and then get flung out of the hole.

I suggest running a little loop of safety wire through the pin to keep that from happening.

Agony prevention, I call it

I have safety wire on mine, works!