In the process of rebuilding the engine, I noticed the starter motor had a rattle. Upon stripping it down I find that the insulator is in pieces. It is square to fit in a groove on the inside of the body - allowing you to tighten up a nut on the outside. Without the piece the 12v post will short to the grounded body and I won't be able to tighten the nut up very well, can't hold it from the inside due to the brush gubbins. Any ideas? Part isn't available but marked in this picture for your pleasure.

Ah yes you stupid boy! Typing in mitsuba brush kit on a site such as ebay/amazon yields a result such as this:

http://www.ebay.co.uk/itm/Mitsuba-2-Bru ... 43de21eec9

.. not cheap. I'll be sure to make sure that the nuts on my post don't seize up again, leading to excessive force being required when loosening the nuts, which must've done the damage to the plastic bit.

I'm spamming my own thread, because this is a lot cheaper and uses the same part number as honda for reference. £25 (more from Honda I'm sure) down to £12.70 + whatever p&p comes to. Starter brush kit for the SM-13...

http://www.motoelectrical.co.uk/types/s ... tsuba-atv/

I'll stop now, I'm happy.

Brilliant bit of info SF. I had exactly the same problem and was going to try fibre or rubber washers but can do the job properly now. Nice one!