About that rear seal leak--I also recently purchased a 240D. It too appears to have a leak from the rear main seal. But upon closer inspection it is leaking around the oil filter stand where it mates to the block. You might want to give it a check.

On the cruise control issue, mine wasn't working either. Before you buy a new amplifier, you may be able to salvage the old one with a soldering iron and a few hours labor. There is a method outlined on the Mercedes Benz Club of America website (www.mbca.org) under the technical section.