That was nasty. Looks like you still need to de-rust that little clip that holds the jack in place, though.
Something to search for: there was a nifty factory accessory plastic bin that fastens on the driver's side of the trunk, over the top of the jack. It's maybe 8" x 15" x 4" deep and is handy for holding small items so they don't roll around the trunk. My 325ix has one, it's the only one I've seen - I should take a picture and post it.
There were a few rusty spots on the (otherwise complete!) factory toolkit in my E24.
I can't remember where I read it, but I got them sparkling -- and a few other metal bits around our beach home -- by soaking them overnight in a solution of white vinegar and water, about 50/50.
And yeah, on the Oregon coast, if it doesn't rust, it dry-rots. Or grows moss.