Hi Chuck,
Many lugers are sold (some by particular dealers...) with whitening filling in everything. In some cases, this is done to hide "sins" and obscure the nature of a stamping and its possible flaws. If a seller will not clean up a piece for me so I can see to the "bottom" of the stampings and/or engravings and the metal just surrouding the characters...my money stays in my pockets...
BTW...Don't forget about the M1929 W+F Bern Swiss lugers...the "S" is factory filled enamel...with some yellowing with age...