stihl br430 crank case floods with fuel

I work a fairly big land scaping company that used Stihl for all of its hand held equipment.  I have noticed this issue with alot of our BR430 blowers.  Randomly some how the crank case will completely fill up with fuel.  It gets so bad that engine becomes hydro-locked.  I can pull the plug and blow out the engine with my air nozzle, and if its bad enough I can position the piston just right I can get air to come out of the muffler which will cause a river of fuel to come out the muffler.  The air filter is also soaked with fuel.  I can blow out the engine clear it of fuel and get it running but its just a matter of time before it does it again.   A day up to a few weeks if lucky.  
 
I have done some research on the internet and found this is a fairly common problem.  Some how the needle inside the carb becomes unseated and fuel gets siphoned out of the tank and dumped into the engine.  As far as I can tell from my research the only fix is to replace the carb.  My question does any one have any experience with this and what is a permeant fix?  I can replace the carb but at $80 a pop for carbs it gets expensive fast especially when you have 100 blowers in our fleet.  
 
Thank you
Gary