I'm A/C trained and specialist in a Volvo dealer... if your compressor has failed, you must replace the receiver dryer too. And I don't know if a MS6 is equipped with an expansion valve or an orrifice tube, but if it's an orrifice tube, you should replace it too. If its an expansion valve, there's no need to replace.
And please, don't put those crappy cans kit in your system! Go to an authorized dealer and put back R134a refrigerant if you like your car.