Don't spend money on it!
I've had my 09 GSA for over 3 years and often got annoyed with it stalling, when changing down, usually in the middle of a junction, or in slow moving traffic, even worse when you've got someone following you...
The solution I found is simple, most bikers tend to blip the throttle as they are slowing or braking to match the revs, this will cause the stall by the pooling effect mentioned earlier. I tend to do sustained rev gear changes when slowing down, this also causes it to stall sometimes. I think it depends on the severity of the braking combined with the blip that chokes the thing up, for want of a better technical explanation.
So, I've changed my riding style, for example; trundling along in top gear, 200 yards ahead I want to turn into a side road, slow down as hard as necessary, only clunking down through the 4 gears as you get to the entrance of the road, aiming to get to 2nd (no blipping or sustaining revs) just before you need to feed the power back in to accelerate as you're rounding the corner. It works every time! No stalling. Same if you're coming to a stop or almost stopping, only select the gear you need for your speed when you've slowed down enough, if you see what I mean...
Infact it has stalled since, but only when I have had to break for an obstacle (an ambulance last time) very shortly after going from 3rd to 2nd in traffic.
Normal slowing down and sustaining revs to gently select a lower gear as long as you keep the motor running (staying smooth) doesn't effect it at all.
If for eg; you're moving along say 30mph in 3rd and you need 2nd to accelerate quickly, blip, match revs, clunk & go no probs because you're not giving it the chance to flood.
Really hope that helps (assuming you follow my drift)

Moreover, hope it saves you from spending your hard earned spondoolies!
Spike