This is a really difficult choice. If you have loads of cash the CL500 is a magnificent beast -IMO one of MB's best looking cars ever and performance and comfort to match.
But 2002 is in a not very good period for Mercedes when cost cutting to survive against foreign competition had been rife. Buy 2003 onwards IMO.
Five litre V8s are not going to be cheap to run and will be difficult to sell on especially once the recession is over and oil goes way up again.
If money is an issue go for the most modern you can get for your budget of either car.
The S class and CL class are built of a combination of aluminium and steel. For the
aluminium components there is, of course, no galvanising process.
All steel panels were galvanised from Quarter 1 2003 production onwards.
During the previous quarter (Q4 2002) the process was gradually introduced
on the production line and therefore some vehicles were galvanised during
this lead-up period, but not all.