ok,,, but something must be wrong for it to only last that long...
IE.... oil not getting to that bearing that went out...or trash in the system..
Since you are not likely the original owner you have little way of knowing if something gave way at some point in the past and left residue in the system... so it would be good to flush it ... just consider it ' insurance'...
Since the Reciever Dryer IS a potential source of TRASH into the system ( the dessicant) ... it would be cheap and good policy to put an inline filter just before the compressor....
The manuals state their case as " if the system has a major leak it is considered compromised" ... which I know makes little sense given it is all under pressure until completely empty... but anyway... they suggest flushing as good procedure for longivity...