They lever arms inside the latches are 0.070 inch soft steel. The pivots for the lever arms are very crude....no ball bearings..and no bronze bearing sleeves. Just a bare steel punched out to form a bearing sleeve. The grease for the pivots attract dirt, which means were I live ...sand. With age, the sand grinds away at the pivots. At the first instance of binding, if you use force to try to actuate the mechanism, the 0.070 inch soft steel levers will bend. When bending occurs, you're hosed.
Of course, if the lever mechanism binds and you can't immediately open the door, it's a PITA to force it open with screwdriver probes.
What I'm saying here is to buy new repro latches. They appear to be of good quality. They're not all that expensive, but before you even start to whine about the price, think about us 68 owners.......there's no repro latches available. If you have a jammed latch, and it's a 69 latch and above, buy a new repro latch, go forth and be happy.