Upon recommendations online I found the Nikon DK-2 eyecup to be perfect for the Pentax 6x7 prism. I bought one and they were right, it worked great. But after the first outting it popped off and got lost. I bought Nikon DK-19 ones as a replacement and they don't fit right. Anyone have luck getting them fitted or is the DK-2 the only way to go?