On the Topic of RUST (other than on Injectors)
Here is a treatment that works time and again without damage (not suitable for deep flaking rust where the metal is exfoliating) The product in some countries is called "Vixol" bathroom cleaner.
it contains Hydrochloric acid 20.00 % (W/W) plus Ethoxylated Nonylphenol 0.70% (W/W).
If you can't find "Vixol" I guess swimming pool HCl is an alternative. The other chemical in Vixol is probably a anti-fungul agent.
Even though Vixol is a bathroom cleaner - it should be treated with great respect :- read this
writeup when the concentration is 33 >>40% :-
Here are a couple of images showing before and after treatment of an engine mounting that rusted up following a leak of salt water from a mixing elbow - the blue arrows merely indicate paint
which remains on the mounting (to show that it is the same mounting)