The steering dampers do wear out but that would not cause the symptoms you describe. It would not cause any rumbling and also it would make the steering feel lighter not heavier. When I first got my C230 I heard rumbling also, and my tires were fairly new also. In my case it is just tire noise. The car is not very well insulated from this kind of noise. If you want to check out the bearings, wheels, tires, you can do some basic tests yourself which will identify some problems. This is fairly easy on the non-driven wheels in my opinion and a little harder on the driven wheels since they don't spin freely. Jack up one front wheel at a time and do a couple of different tests:

Spin it and look for anything out of true or out of round. Look at the rim edges and the tire tread and sidewalls as it spins. Next test is grab the tire at 3 and 9 O'clock and move it gently. You should feel no play. On mine I felt some play "clunk, clunk" which turned out to be worn inner joints on the center link, which is important for handling but will not cause the symptoms you describe. I just mention it so you don't make wrong assumptions. Then grab the tire at 12 and 6 O'clock and do the same thing. On mine I have slight play in this direction, but the runout is still within spec.

This is all assuming that you want to try to figure it out yourself. If not then just take it to a good shop.

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra