I don't think this is very complicated really. I only buy used holders and only use the ones that do not leak in direct sunlight. They are easy enough to test. I have about 40 good holders (4x5). Some I have been using for decades. The only ones I have had to retire were ones I did dumb shit with like dropping one from the roof of a 15 story building or dropping one in a stream (the film stuck so bad in the rails that I could never get the rails clean enough again).