I went through about three months of hell with my 240 with similar problems. Knowing they sometimes manifest their ills in strange ways, I started with the driveshaft, but that was completely wrong, did nothing to help. Going from there to the standard stuff, I checked my front rotors and found them very blue in some spots. Thinking they were overheated at some point, I just put new ones on. This helped a great deal, but though the shudder was now inconsistent, it persisted. I took the car back to my "utility" tire shop, the place I go just for flats and stuff, and had the tires balanced. The shudder changed completely, but did not go away. Went from shudder while braking at high speed to no high speed shudder but a 15 to 30 mile an hour shudder. I took it to the shop where I buy my tires when I need new ones. They put the tires on the machine, one at a time, and the manager ran the machine with a face shield on and the safety overridden so he could run it open. He put a special guide on the machine that tracked the perimeter of the tire. Though the machine showed the tire/wheel combo in balance, the tire was out of round. If it were a little, I could have had them "trued". That is, shaved to make them round, but it was way too much. The rims and tires had been purchased used. I never noticed the cracking on the inner side wall as well. He said the tires had probably been sitting for ages either on a car, or standing up and had flattened. Bought new tires....shudder disappeared.

DS