Hi Jean...ok, the best place to go for information is to the Yahoo groups Davis VF and Davis Sewing Machines. The Davis VF group was started just to cover the Davis Vertical Feed machines. The second one covers all the Davis machines. They have TONS of information. I have an 1890 Davis High Arm VF1. My finish looks like yours, which is basically really bad. The finish is extremely delicate and fragile, so only use sewing machine oil to clean off the dirt, and don't try to do anything else to it. You can clean the metal parts with Barkeepers Friend, which comes in a can like Bon Ami, and is gentle enough to clean the metal.
Jon on the VSMS thread is the one who is the resident expert on these machines. You got a HECK of a deal on this!! These machines are rather rare!!