As Zont says, preparation is the key regarding metal work. I found rust in the vicinity of what was obviously visible.
4.5 inch wire wheels/flap wheels on a grinder is good, and for smaller areas a dremel style tool and a variable set of attachments.
There are loads of solutions but prep is ALWAYS the key.
Once rid of the rust and use something like Bilt HAmber 80 to treat and kill the remaining rust in pits, neutralize bare steel and form a suface over the area.
Overtop with maybe an epoxy mastic paint. THEN apply Waxoyl or something to repel attrition as it's a rubbery finish..
Deffo not duck oil as even if you did then waxoyl, it wouldn't stick to any oily surface. Needs thoroughly need de-greasing first.
Depends whether you want to delay it for a bit, or treat it properly. Deffo not duck oil before applying WAXOYL though. Not many covering compounds will stick for very long on an oily surface. Everything says de-grease.
Best of luck