I have a Zorki 4. Looks like new, Jupiter-8 too. It's been sitting idle for at least 16 years, probably more. It's not so much that it has problems with the slow speeds as it's replaced all its speeds with one, sloooooooooooooooooooooooooooooooooooooooooooooooo oooooooooooooooooooooooooooow. I look at its curtain and it gives me this big and long yawn, I get sleepy every time.
I may work the shutter a bit if I ever get bored enough. It's too bad, it's a cute camera (no, it's not).