When you put the camera in a dark place for some time, the vulcanite will darken again and spots will disappear. A miracle! However, the vulcanite will not become black, but in the dark it gets an even, dark grey tone. Do not worry, the vulcanite will keep it's smell (sulphur).
Never recover the camera unless the vulcanite is very incomplete. The camera looses its attraction and value when it is recovered.
It is not possible to damage the vulcanite with oil or grease. In use, it gets smoother, but that takes a very long time. You can tell if the camera has been used a lot when the vulcanite is smooth. On parts that you cannot touch it you can still see its original texture.
The vulcanite - guttapercha - is a very interesting material made from a special composite rubber. This material was used for isolation in a period that plastics were unknown. The kind of guttapercha that is used on Leicas was also used for the isolation of telegraphic cables in the deep sea in the 19th century. Golfballs are made from guttapercha too.
When you want to remove the covering you'll have to disassemble the camera completely and to heat the sleeve. Then the vulcanite is very easy to remove.