Yes, I would buy it (especially for 25 dollars). The only problem that I know with the Rocketeer is that the door that opens at the front of the head breaks off of the machine easily. I think if a person is careful with that door, then they shouldn't have any problems. In fact, I would pay that price for the desk alone. I may be wrong (because I've never had a 500A) but I believe that your 401A will fit into the desk. If I remember right, the 500 is just like the 400 except for the shape of the head. I have two 401s and one 403 because I like the way they sew.
You should be able to clean up the white stuff on the gears. One of my 401s was like that but we were able to able to get the cams unstuck and everything cleaned up.