Volvo does mention refurbishing the rustproofing on your car. In the owner's manual they mention two types of rustproofing that can be touched up.

I reccomend that you take your car to a dealer and get their reccomendations.

Any good body shop can give you an estimate for fixing up your car's body, get a couple for comparison. If you do decide to paint your car consider a color that is unique, your friends will think that you bought a new car.

Two things that you can do are;

1. Check all the drains on your car and clear them if they are clogged.

2. You could scrape and sand small spots of surface rust off the body and treat them with rust converter. I did have luck with this process on a 1 square inch rust spot on the front fender of our '88 745 GLE. Although the offending spot does not look as if a professional repaired it, it has not changed for the worse in over two years. I painted the rust converter with touch-up paint aftyer the converter dried properly. I spent a total of 30 minutes or less on this repair.
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2 8s & 2 7s 600,000 miles total