Phil_F_NM
Camera hacker
My understanding has always been that the 105 both F and RF both use bronze not brass, so need little or no grease. Careless use of grease which are corrosive to bronze gears may be part of problem.
The RF version of the 105 definitely is all brass but I think the inner helicoid on the newest version of the SLR lens may be aluminum alloy. A few years ago I worked on an 85mm f/1.8 Ai that had both metals AND they were in contact with each other. This is a big problem with helicoids since mixing metals can often lead to galvanic corrosion. The 85mm I mentioned was completely locked up because it had either orange juice (with pulp) or V8 tomato juice spilled on it which literally ate pits into the alloy helicoid but the brass was fine. Petroleum lubricants that break down into acids and fatty solids can do this too as was previously mentioned.
Fortunately, the only Nikon RF lenses with mixed metal helicoids that I know of are the FSU lenses but they are usually so over-greased that corrosion isn't a problem, cleaning them to get them to move smoothly is. Now, even Leica mixed their helicoid metals in the 90mm thin Tele-Elmarit and the 90mm f/4. When I got into that lens I was very disappointed to see the mixed metal helicoid.
As for sending a lens to me to work on; I'm flattered. I would do it but I recently moved a few times and I don't have the work space available that I would want for the lens of an RFF member. If the lens is being sent to the US, Youxin is a good repair tech in Canton, Mass.
Phil Forrest