Possible buying an 02 L w/18,000 miles
#1
#2
As far as parts, check any of the supporting vendors and they should be able to get you in the 12's. As far as drawbacks, there is the price of gas, and well, thats about it. They are a kick to drive. It's always fun getting the jump on uneducated people with a TRUCK. Good luck with the truck if you get it and you can always find a lot of help here on the boards if needed.
#3
Only thing to be aware of on an '02 is the possibility of spitting a plug. Heads only allow about 4 threads of plug. As long as there in tight, everything should be fine. I have a friend that had his replaced. Might want to see if this was done on the one you're looking at. Otherwise, hit the gas and hold on.