According to Kelly Blue Book, it's $29,500 trade-in value and $43,000 retail. This is for a '87 S500 4D sedan. It's more if it's a coupe! The final price should be some close to trade-in value.
Sunshine, never heard of a successful repair using radiator stop leak. But there is something that does
work very nicely. Check out this link: http://www.cryochem.com/CRYOseal.html