OK, so I now have the answer to a previous question of mine; what is the third hole (between the two drain plugs) in the bottom of the engine for, and should it have a bolt in it? ...mine did when I got it, but it let a load of water out when I removed it.
The hole, indicated here:
...is a drain hole for that chamber above it.
That chamber seems to do nothing other than collect water (or any thing else) that comes through this hole that is behind the stator:
So it probably doesn't matter too much whether you have a bolt in there or not, but if you get water in the engine you probably want to remove it to let any water out.
