if the shaft is badly scored allthough being single acting that doesnt really matter, have a new shaft made much cheaper than trying to hard chrome or resurface them. and not all citric acid is food safe, only under certain concentrations is it food safe. the acid in nearly all cola drinks is phosphoric acid actually yes coke does use citric acid in the recipe.

Morning trainzkid88, I bought my citric acid powder from a wholesale food supplier in a 20kg bag about 8 years ago, I think it was about $100, still using that first bag, I'm happy to handle it with my bare hands, never even get a tingle, unless I've got a cut, my Mum used it when I was a kid to make lemon syrup cordial, I used to help her, plus drink more than my fair share of the syrup, probably explains why I'm going bald 60 years later. LOL

I've heard of guys crushing up a bunch of lemons to create a acid bath for cleaning rusty parts, also guys Stateside using any cheap sodas rather than buying "expensive" Coke, knowing most sodas have citric acid in them.

cheap $2 a bottle white vinegar works well too. here's a side note high concentration acetic acid is flammable, well vinegar is a brewed product. it's just i have worked with concentrated citric acid. and dad got the lab chemist at work to order it in. he also ordered some for a model engineer friend so he could pickle the copper boiler for a live steam model he was making it needed pickling before silver soldering. i have had chemical burns its not fun.