Having a few problems with this one.  First of all, the ignition
switch failed on Saturday (wouldn't spring back from START position).
I replaced the ignition switch yesterday, but I now get a horrible
grinding noise when I switch the engine on - as if the starter isn't
retracting.   I will turn the engine manually to see if there's any
visible damage to the flywheel teeth, but I think the starter motor
needs replacing.  

And here's the problem:  I can't see any bolt heads on the front of
the starter motor:  looking at it from underneath the front of the
car, what I can see is a semicircular end to what should (?) probably
be a bolt head.   Anyone come across anything similar?   Could the
bolt head have been partly sheared off?

thanks in advance for any suggestions.