Yep, the acid is a bad idea. For removing rust and leaving it nice, I'd use
naval jelly. Goop it on, wait, wipe it off.

If you'd rather, you can completely immerse the whole unit in a solution of
vinegar and table salt - as much salt as can be dissolved is just right. I'd
suggest you completely disassemble the unit for this idea. You'll find its
full of swarf and dried out grease.

Karl