It is never recommended to repaint it....
For some reason that realiy affects the value, not as much as a re-wrap, but still not worth doing if you plan on ever selling them.
Also consider that no one will ever see it, so it is not the most important part of a restoration.
In many cases cleaning them is how so many date stamps were removed from drums...
So you should first protect that area with tape, and or put a little piece of plastic over it and tape around it....
Then with any mild cleaner and a soft sponge just wipe it out.
Make sure the sponge is not overly wet and that you are not using an abrasive 3M sponge. Soft car cloths and other all cotton cloths will work well also.
I used to use windex when I had drums with that interior, but I do not remember how well it cleaned and or if that was good or not.
Also, soft scrub is a great cleaner for drum heads and I have also used the non abrasive formula on shell interiors and it really does wonders to the interior..
You do not want to do a lot of scrubbing and or rough work on the inside of the shell, so start with a small spot and run a test prior to jumping in full force..
Others probably also have their own way of doing things and all probably work equally well.
David