It wasn't a lubricant problem. Only a minority of lenses suffered from it. And it was due to the glass formulation used. Early 50's Elmars were quite prone.

That isn't to say that Leitz lenses don't also have fog problems from lubricant and general atmospheric crud, as do all lenses.

The lubricant fog can be cleared away, the fog due to glass problems can't.

It seems most fog problems in Leitz lenses are due to lubricant and few people have seen the glass problem.