Thanks all for the advice. Having taken a good look at my garage door, it looks like the consensus is right... my home is almost 25 years old and it does indeed appear like the plywood is separating. I've already done a fair amount of sanding and I don't seem to be getting very far. Besides, the door seems to have more moisture damage than I expected. Now the question is do I go for steel vs. aluminum for a new door. I've already had a couple of estimates and it looks like the aluminum is substantially more expensive than steel. The steel doors do come also with at least a 10-15 year warranty. Any advice there?