Never use 3in1, WD40 or other household oils on a sewing machine. Good sewing machine oil is inexpensive, even Walmart carries Singer oil.
The foot controller is super easy to change. A lot of people like the electronic controllers like the one shown here -
https://shop.sew-classic.com/Foot-Co...p-SCE168FC.htm
It's easy to disconnect the two wires inside the old controller and simply reconnect them to the new controller. It doesn't matter which wire goes to which side.
Does your walking foot have a wide needle slot? If it does I don't see why you couldn't use it on this machine. The feed dogs are in the same place and are shaped the same as any other machine. If any foot has a wide slot for use in a zig zag machine it can be used with a left needle machine. The straight stitch foot is the only one that's machine specific that I know of.
Cari