My 1990 740 started doing something like that at 144k . The front of the engine sits on two engine mounts that are filled with liquid. Over time the dampening effect of the liquid is lost because the liquid leaks out. At that point the engine may not be yet sitting on the cross member but it's sitting directly on the frame for all purposes.
The transmission mounts are worth looking at too, particularily the one on the little cross member. Are there exhaust leaks anywhere including the over-the-axle pipe ?