Ive been using vallejo primer for a while and I just used up my can that ive been using for a year now. A guy that plays at my LFGS says vallejo primer has gone to crud and it comes out very grainy now. Ive had primer come out grainy before and it was human error i tried to primer when it was to humid. Has vallejo aerosol primer gone to crud or was this guy just using it in bad conditions? Ive also never used it on PP plastic does it have any weird effects on it?