The early Type Is and Type IIs used to suffer the same fate when the starter
bushing was bad.  Don't know if the diesel trans has one, but worth a look.  
It is pressed into the bell housing where the starter gear shaft fits.  To
pull it out, look for a roundhead bolt with a head about the same size as the
hole in the bushing.  Stick the head of the bolt in the hole in the bushing
and try to catch the edge of the bushing and pry it out.  Slip it over the
starter gear shaft and see how much play you have between it and the shaft.  
Usually a bad bushing will be chipped and scored and have lots of play.

Tom
'71, '78 and '85 Westys, '91 Carat