I sent both my D3s and D3x in for cleaning, and to fix the vertical AF-ON button on the D3x. When I removed the RRS L-bracket I noticed an oil film on the base of the L-bracket. I don't know which camera that L-bracket was on. The oil film is the footprint of the base of the camera. It is not water.
The cameras reside in a Pelican case or on a shelf in a closet. I have never spilled anything on either camera that I know of.
This is the first time this has happened and I am just curious as to the origin of the oil.
Apparently no one can think of any possible sources for the oil.
While there is a tiny bit of lubrication for some of the moving parts – I think it is unlikely that there is enough oil inside the camera to get what you describe - Therefore the oil must have come from an outside source that you didn’t notice at the time .
Could it have been something like sunblock or similar from the bottom of a camera touching you or someone. It only takes a tiny, tiny amount of some of those to mark rubber.
Alternative #2 could it be something on the camera actually cleaned an area of the L-Bracket slightly. Some residue from the shop visit that they use for cleaning or preserving that was still there, and changed the appearance enough to look like oil?
first is not likely, but a good thought. the bracket is on all the time.
2 is a possibility. I asked the shop to take a look at the base of the camera to see if there is anything on it. I did not look at the camera base because I didn't see the oil on the bracket until after I had sent the camera to the shop.