I have a couple of cameras / lenses that need helical lubrication. One is a zeiss super ikonta, the other an old lens. Both have a brass thread inside a harder metal threaded sleeve for focusing; I need to clean these and relubricate. What would you recommend to make the focus smooth again? Some kind of synthetic grease, or something else? I don't want to use the wrong lubricant and mess up either camera or lens with spills, seepage, or vapour, and I don't want to use something that will gum up with age. I will only undertake this if I can do a professional job that will not degrade the camera or lens. (I'm skilled enough at disassembly, cleaning, and reassembly - that's not a problem for me, I've done it many times with many cameras). What would you recommend?