After the purcase of my new e36 i found that there is a little rust spec maybe 1cm by 1cm at max that is on my rear quarter panel.

I'd prefer to spend the money and repair the entire quarter panel (my car is cosmos black, so itll look much newer), but it'll probably cost about 1k to do that.

Any suggestions on what to do about it?

Level the paint (compound, polish or wet-sand) then apply
Rust Inhibitor:
POR-15 is a paint-like substance which acts as a total rust inhibitor and is also very effective as metal filler. It chemically bonds to rusted steel to form a rock-hard, non-porous coating. POR15 won't crack chip, or peel and works by isolating metal from moisture, without moisture present, steel can't rust. - http://www.stoprust.net/ (http://www.stoprust.net/)