The filler found on older machines comes in two flavors- either crumbling off at the slightest touch or absolutely welded in place and indivisible from the casting. Only problem is, you usually run into both on the same machine.
I'll confess that I'm prone to buying the machine I want and figuring out the issues later, rather than waiting to find a machine in good shape; it drives my wife nuts, but it generally works out fine in the end. I've often wound up with a machine because it was historically important ( I collect Porter Cable machines) or I felt sorry for it, only to find it become indispensable in my shop.
-James Huston