Use a rust eater that doesn't contain acid ie a chelating agent. The market leader would be Evaporust https://www.amazon.co.uk/Evapo-Rust-...5593200&sr=8-1
It's not cheap and other products are available but you can't damage the good metal by leaving stuff in it for too long. Best to thoroughly degrease the part beforehand, so it doesn't contaminate the fluid. Also, it won't work if the leadscrew is greasy. Once done, you can brush it off and rinse it clean.

You can make your own chelating solution but that could be a rabbit hole of its own....