My oil level was about mid way between low and full, so I topped it up. Does the engine oil lubricate the starter gear? Is it possible that my oil level was just a bit too low?
I would say no. If you're above the low level you're oil level is OK.
The engine oil doesn't lubricate these gears. They are on the outside of the crankcase.
Have a look at this diagram: http://bit.ly/1gKIUTp
I had a similar problem with my GS500, the function of the gears is almost identical. You want to have a look at 13193. That is the assembly that engages and releases the gears using springs, and centrifugal force respectively. When the gears are stopped, the springs (92081) push the pins (92043) and rollers (92122) into the centre. When the starter spins, the rollers rotate and slide into place and the outer gear becomes engaged with the inner piece (16085) due to friction and the rollers becoming wedged. When the engine fires and the crankshaft spins faster than the starter, the rollers rotate the other direction and disengage. With the gears spinning fast, the centrifugal force on the rollers and pins overpower the springs, and the rollers move toward the outside allowing the two gears to rotate independently.
Check everything looks as it should, and make sure it's well lubricated. Its worth finding a download of the service manual and reading it to see if there are any special instructions for servicing this.
...or just pay a shop for a diagnostic. :/
Prob have an answer for you in 10 minutes.
Thanks a bunch spray____, this post will be very very useful. I will report back with my results (hopefully on Sunday).