Section of Rear Spring Exposed
 

Since I have springs on the brain (front springs on 98 getting replaced), I looked at the springs on the 99 and noticed a two inch section on one of the rear springs that is exposed (i.e. black coating came off) and has surface rust. Am I correct to assume that it's worth my while to put some POR-15 on there to delay the inevitable?

Generally high carbon steel like in springs rusts slowly. I might just dab some heavy grease on the area. Then check it once a year to see that it is still there.

rattle can rustoleum - touch up as needed

x2 on the rattle can rustoleum.