Same here. Have used Lincoln and several other brands. Decided to try the cheap China ones - see what they will do. Doesn't seem like I ever replaced as many couplers as i have in the last few years.

I found out one thing that will ruin them - paint. Had a nearly new coupler go bad so decided to take it apart and see what gives. Was full of green paint chips off of a new machine I had greased. They must get some tiny Vietnamese lady to assemble those suckers cause I was never able to get it back together, hard as i tried. Decided my time was worth more and finally chucked it - of course it couldn't be one of the cheapies, had to be a Lincoln.

It helps if you can find a place that caries the 6 or 10 packs. They are about half price as buying one at a time. 

John