what are the common faults

On August 2012　I　recieved my Celcius MX3 training weapon .The gun has been in for repair 3 times todate and is now back for a forth time now .The first repair was a hop issue (bb's were never consistant), the second was a cylinder issue (air nozzle and bb,s shattering although never had these issues in any A.E.G ive owned in the 15yrs of playing - using "blaster devils" by the way , the third was hop unit (as before) and cycling issue (gun would stop mid-cycle) and upon advise of the shop I paid for the upgraded hop unit(on a wheel as opposed to using the hex key), I recieved the gun back and still the hop unit continues to be an issue along with the gun failing to cycle .To date since recieving the gun I have never been able to use it for one single whole game without issues/faults. The issues I have experienced are they common faults from the manufacturer only I just seem to keep throwing money at a broken gun that I never had the chance to play with. ( U.K based player)