I did try this:
Four bottles of Aldi vinegar (I nearly dropped the lot in the shop):
Use some kind of container and put rusty stuff in (this case, one v.rusty caliper, one new but surface rust caliper):
Put vinegar on:
Couple o' days later:
The 'clean' caliper had a surface of rust from the other caliper, but it had removed the original surface rust, and the oil/grease:
Tougher rust, wasn't so good, but the rust felt looser:
Wire brush brought some of it off:
Let it dry out with boiling hot water, and then gave it a proper going over and then painted it.
Did a couple more new ones, which cleaned the grease off:
The verdict = good for slightly rusty components, not that great on very rusty stuff.
Will try home-made electrolyting next!!