It's not difficult to whip the starter motor off and check that a) it's rotating freely, b) that the return spring is not kaput, and c) that the pinion is able to run freely both ways. Often even a little a bit of **** on the shaft will prevent it from working. Clean all the moving parts and then try it off the vehicle using a set of jump leads directly from the battery. If it doesn't give a good kick when it starts to spin, it would appear that it could do with a rewind and refurb.
By the way, I use a 230A/Hr battery!
Hope this helps.
OSD