Hi,
I've got a problem with my MIK L2500, just realised that there are some patches in the back that are unfinished, and are are starting to get dark.

The back of the neck is satin finished.
Does anybody know what's used to finish the back of the neck, would it be OK if I use Tung oil??
The maple fretboard also has a satin finish, but it seems to be a poly coat of some sorts but I'm not sure, the fretboard finish seems fine but I would like to know what it is for future maintenance.
Thanks