That’s what happened to my 2006 Core Duo MacBook after about three or four years of use. It was an excellent laptop that was quite user-serviceable (I upgraded the RAM and hard drive), but I did have problems with the palmrests, and the Ethernet port stopped working after four years.
It was my first Apple laptop and I have fond memories of using it during my college years.
I had one of those machines in university too and had the same stained/cracked palmrests. That said, I also paid for extended AppleCare and had the whole top case swapped for free multiple times throughout the three years that the coverage lasted.
When I was a broke student I would buy MacBooks with broken palm rests for a discounted price, drop them off at Apple for a free repair (under extended warranty) and flip them for a profit. Three hours of my time turned into €100 profit. Minimum wage was €6/hour back then.
Did the same years later buying up first gen iPod Nano and trading them in for sixth gen because of the battery recall.