I have worked for Sheriffs, and with Deputies who have left long guns in their vehicles for their entire term they served - I had to repair one that was so rusty you could not open the bolt, it was a full auto Ruger.
OTOH, just after I left the Memphis area, the FBI lost a whole Suburban load of MP-5s, and one PD, who I did not work for but knew some of the offiicers, lost a crate of Uzis which they were considring for their SWAT team - the crate was sitting on the loading dock, never got issued - I have no idea if any of them showed up. At the time they were considering issuing Beretta 92s and the Uzis for SWAT - they ended up not adopting either.
I'm neither for or against leaving a long gun in a vehicle - it will just depend on where and how the vehicle is stored. But I would advise checking it every month at least to make sure it is in working order (if it is not kept in a case I would store it with some tape over the muzzle - bugs have a way of builting nests in dark places!).
Riposte