Simon.
Painting of the engines did not`t have a navy code and was for us anyhow something which was up to the engineers, sometimes overruled in extreme cases by the chief engineer. One rule however, moving machined parts,springs, shafts,handles etc was always kept shiny metallic. Painting inside the valve rockerarms would be OK particularly if you have a metallic rim as seen on the picture. On Laboe U 995 painting is far overdone and moving parts are painted to such an extent that they look like they are casted (intgrated) to F.I. a fulcrum.
Tore