Well Mav, I have been screwing around with the pump for longer than I should have, and here is what I know:
The impeller mod isn't going to help. It seems to actually make it worse, but I can't be sure about that. The shaft mod does not apply to this model.
Here is what I suspect:
On either end of the impeller rod, there is a black rubber cap. This snug into the holders on either end to keep the impeller in place, yet allowing it to move freely. It also serves to prevent the magnet or impeller blades from knocking into the walls, hence preventing wear and "rattling".
The problem on mine at least, was that the "front" rubber cap did not allow the rod to spin easily compared to the "back" cap. The difference was dramatic, and investigation showed a lack of black grease within this front cap. Unfortunately, I don't have any real grease handy, but I suspect this is the problem.
If I put it back together without the black cap on the front, it started every time, first try. Course, it rattled like hell. So I grabbed the nearest lubricant available (relax, this post is rated G)- Extra Virgin Olive oil. I lubed the black cap up pretty good and put it all back together, and with a few exceptions, it started right away. Even when it didn't it kicked in after a few seconds.
Now the effects of the olive oil wear off quickly, since it is far more viscous that standard grease- but I think it is conclussive enough for you to try it if you have some grease handy.
Good luck!
Mechsiah