While tracking down a power steering fluid leak on my 2000 CLK320 (68K miles), I'm pretty sure that my harmonic balancer is about to fail. When the motor is running, I noticed a wobble at the crankshaft pulley (not the pulley itself) because the balancer is warped by about 2mm.

I have an appointment to have it replaced by the dealer but it's about a 15 mile drive that I can do at speeds under 50mph. My question - would you have it towed or would you drive it?

I would have it towed. Simply because if it comes apart more, it can chew a hole in the oil pan fast.

Check with your dealer, I'm sure they are still coveren under warranty. My 2000 ML320 had the same issue(same motor, M112). The dealer should pay for the towing and the repair under goodwill. Talk to the general or service manager not the service adviser. They will almost always say no.