GMC 1994 Yukon Owner's Manual page 322

Weatherstrips
Silicone grease on weatherstrips will make them last longer, seal better, and
not stick or squeak. Apply silicone grease with a clean cloth at least every
six months. During very cold, damp weather more frequent application may
be required. (See "Recommended Fluids & Lubricants" in the Index.)
Sheet Metal Damage
If your vehicle is damaged and requires sheet metal repair or replacement,
make sure the body repair shop applies anti-corrosion material to the parts
repaired or replaced to restore corrosion protection.
Foreign Material
Calcium chloride and other salts, ice melting agents, road oil and tar, tree
sap, bird droppings, chemicals from industrial chimneys, and other foreign
matter can damage your vehicle's finish if they remain on painted surfaces.
Use cleaners that are marked safe for painted surfaces to remove foreign
matter.
Finish Damage
Any stone chips, fractures or deep scratches in the finish should be repaired
right away. Bare metal will corrode quickly and may develop into a major
repair expense.
Minor chips and scratches can be repaired with touch-up materials available
from your dealer or other service outlets. Larger areas of finish damage can
be corrected in your dealer's body and paint shop.
Underbody Maintenance
Chemicals used for ice and snow removal and dust control can collect on
the underbody. If these are not removed, accelerated corrosion (rust) can
occur on the underbody parts such as fuel lines, frame, floor pan, and
exhaust system even though they have corrosion protection.
At least every spring, flush these materials from the underbody with plain
water. Clean any areas where mud and other debris can collect. Dirt packed
in closed areas of the frame should be loosened before being flushed. Your
dealer or an underbody vehicle washing system can do this for you.
Chemical Paint Spotting
Some weather and atmospheric conditions can create a chemical fallout.
Airborne pollutants can fall upon and attack painted surfaces on your
vehicle. This damage can t.ake two forms: blotchy, ringlet-shaped
discolorations, and small irregular dark spots etched into the paint surface.
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