What a drag. The same thing happened to me. The black K-50 started failing in August of 2017. I had to fix it quickly 'cause I was about to go on a trip to Japan, so I ordered a "white" solenoid & did the fix on my own. It took me about +-3 hours to do. In June of 2018, the red one stated failing. I did the same thing. They've both been trouble free since, even the black one with the ultra shoddy soldering. Haha!
I did a much better job on the red one.
But yeah. It's annoying that I had to fix them on my own. Mind you that both of these had about +-25,000 actuations or so before failing so it wasn't due of the lack of use.