Hello, I have a Voitländer Nokton 35mm M mount lens that has residue on the back of the front element from moisture. I've tried disassembling it to clean and I can't seem to remove the front element. The retaining ring spins but won't unthread. I've tried completely disassembling the lens from the back but I'm unable to access the front element that way and can't find any information online. Is there any information available on how to do so? thanks!