[dsraven]

prolly the latch is worn out but without a few pics we are guessing. first, how does the door fit in the opening without the latch being latched, like as the door closes just before the latch engages does the door line up or does the door fitting rely on the latch to bring the door into the closed and fitting position? is the door seal tight so the door needs to be slammed to get the latch to actually catch?
best idea is to remove the striker and see how the door actually fits the opening. adjust hinges as required and then look at the seals. the door should seal when the body lines up. some new rubber is stiff so the latch takes a beating to hold the door against the tension of the thick rubber. pretty common actually. the door skin should sit level with the body like you would expect. if the seal is too thick i recommend soffseal but thats just me. others have different favorites that still compress easily and seal. when that is figured out look at the hand lever and linkage for wear binding etc. when all good look at the outside door handle for wear binding etc. when all good look at the latch mechanism for wear, springs dirt etc. bench test it a few times so you know how it works and why it may fail periodically. when all good install the latch and striker and adjust the set up so the door sits even with the bodywork. then test the set up a bunch of times. sometimes it's just in need of a cleaning and lube and sometimes it's just plain worn out. one thing that a lot of guys do when adjusting the doors is expect the latch to magically bring the door into align with the body, like lift it or bring it down into the final position needed. that is not what they were made for. a latch is just that, a latch. it isn't a body man in disguise. using the latch for the final alignment is just wearing the latch and striker out.