A neutral PH, "color-changing"wheel cleaner would be the thing to soak the lug nuts in to convert the brownish rust deposits to purple residue which can be washed off with water. This would also save much of the zinc/aluminum fininsh as possible. Maybe require multiple applications and to speed the rust stain removal, I'd suggest wire brushing by hand with brass or stainless wire brush on the soiled areas. If not handy, yes, you could use acid-based cleaners. They can be hard on pure zinc, but the dip-spun coatings on these Porsche fasteners have layers of aluminum in addition to layers of zinc, so maybe would be OK.
https://en.m.wikipedia.org/wiki/Zinc_flake_coating
However, before trying chemically remove the iron oxide stains, I'd use a strong solvent like anything with acetone in it (brake parts cleaner, carb cleaner, lacquer thinner) with a paper towel to wash off any loose dirt and old oil or grease residue. This strong solvent won't harm the bolt in any way, although it's hard on your bare hands, and will tear up even chemical resistant gloves. I've had good results with nitrile gloves and
chlorinated brake parts cleaner, although that stuff seems banned in places like California. I have no idea about Canada, but it is available here in Washington state.
After they are cleaned an dried, I'd suggest spray coating the outer-appearing surfaces (not where the bolts seats or the threads) with a high zinc content (> 90%) cold galvanizing spray. Give time (and maybe heating?) to allow the cold galv to cure and harden.
Then, apply a thin coating of gray colored anti-size on the threads and reinstall.