I have a 2013 Ram with 29,000 mikes on it, the 5 MPH max in the next 200 mikes def systems needs serviced see dealer message came on, took to local dealer and they are telling me my def is testing poor and that it has started to crystalize and now they are telling me the fix is to replace tank, pump, injector, the part the injector injects into, I have read about def shelf life, but can't seem to find anything about the life of it after the container is opened, this truck is not a daily driver and sometimes will sit for 2 weeks without moving, is it possible I have def going bad in my tank? I just added def about 4 days ago and it was a fresh jug I just bought, the last time I added before that was February. Anybody have any ideas? Thanks in advance.