Snow Blowers

Snow Thrower 10527SB-LS P/N 96193002800 2008-09 version, purchased Dec. 2008.  One year and two days ago, dealer installed "Control Shaft Kit 532 41 98-77," a kit that I believe refers to replacing the impeller control shaft, P/N 532 40 61-09 when I brought it to them because the impeller stopped turning.  I also had them replace both belts, as a precaution.  Today the impeller belt popped off.  When I opened it up, I looked for what may have caused it, other than just maybe having loosened due to belt stretching.  (In my 4 winters experience with this unit, I've found the impeller and drive tension need adjusting at least once every season, when the drive or the impeller starts losing its grip ... slow or stopped drive or slow/weak impeller throw.  And the adjustable space runs out long before the belts are worn out ... annoying.  But that's another matter.)  Today's investigation found the idler brake arm (532 42 21-11) had popped off (forward) of the end of the control shaft (pushes the idler pulley against the belt to engage impeller).  I put it back in place but it seems likely to happen again.  The arm sits tenuously at the very edge of the end of the shaft.  It is working fine for the moment, but something does not seem right.  There is NO space at the end of the shaft tip.  The idler arm is RIGHT AT the tip.  So my question is: is there an upgrade kit to improve the contact/retention between the shaft and the arm?  Or possibly did the dealer install the wrong shaft?  Their invoice says they installed a control shaft KIT which has a difference part number than the shaft itself (see above).  Was that the right kit?  OR, is there something wrong with the idler arm?  The way it is mounted to the bracket - on a pin - allows the arm to tilt forward/back easily, due to play in the fit of the pin, seeming to increase the chances of popping off the shaft.  Seems to be the way it comes from the factory.  The parts breakdown does not show anything involved that may have come off or broke.  The idler arm spring is fine.  I don't get the whole idea of the shaft just resting against an arm with sloppy play in it.  The shaft should go through the arm with a pin to keep it in place.  (When I'm King of the World, a lot of things are going to change.)  Any help/advice will be greatly appreciated ... especially if before the next time the arm pops off!  Thank you.