First thing I do is apply grease. Good old fashioned grease. WD 40 may work in a pinch but eventually will not last. Of course grease wont last forever either, but I seem to geat at least a season out of it. Apply on the strike plate and the sliding bolt / latch mech.
"DON'T FORCE IT - GET A BIGGER HAMMER'
"Paul & Laurie"
2013 Columbus 340 RK
2013 F350 Dually 6.7 Diesel