When Neil Young sang ''Rust Never Sleeps,'' he might as well have been croaking about the slow but inevitable deterioration of Minnesota automobiles. Because the state uses salt on its roads, vehicles can decline from showroom beauties to embarrassing rust buckets in a hurry.

For years, the easy answer to the deterioration was rustproofing. But for a variety of reasons, the rustproofing business isn't what it used to be. Lindsay Fraenkel, store manager at Ziebart in Minneapolis, says leasing has taken a big chunk out of his rustproofing business.

Even dealerships aren't pushing rustproofing as an option as often as they used to. Part of that has to do with cars being made with longer-lasting galvanized steel.

Manufacturers' warranties for protection against rust perforation also are longer. Most warranties provide corrosion coverage for five years, and some are even longer, such as General Motors (six), Mitsubishi (seven) and Volkswagen (12).

So is rustproofing a thing of the past, even in Minnesota? Star Tribune auto columnist Paul Brand still recommends rustproofing for new and used cars, especially for anyone who plans to hold onto a car for more than five years.

Cars don't generally show rust until after the fifth year, about the time many manufacturers' warranties expire. But consumers may be disappointed to discover the kinds of exclusions in corrosion coverage, including rust caused by ordinary elements such as sand and salt.

Examine the warranty for exclusions, such as surface rust, rust caused by industrial fallout, areas damaged by stones and debris, corrosion caused by sand, salt and hail and tree sap. Some warranties contain vague phrases such as "rust caused by abuse or misuse" or "lack of maintenance" that may prove to be catchalls to deny coverage.

Some people may be tempted to wait until the sixth year to have a vehicle rustproofed, but by then it may be too late for prevention; it could mean a body-shop repair instead. It depends on how the car has been maintained up to that point.

When should you rustproof? Generally, if a vehicle is new or less than three years old, it's a candidate for rustproofing if the owner wants to keep it for more than five years. Otherwise, a person may want to let the next owner worry about rust.

Is it worth it to rustproof a car that will be sold before rust starts? An after-market rustproofing may enhance the value of a used car somewhat. And most rustproofers will allow the warranty to be transferred to a new owner for the first five years.

Price and warranty