The big difference I noticed between the new and old mounts: the new (functional) mounts allowed some engine movement. The fluid had drained out of the old mounts, so the engine was just sitting on hard rubber. While this didn't allow much engine movement, it did transmit lots of vibration.

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alex

'89 765T, 178,3xx mi

That sounds about right. If there is clearance between the rubber pad on the crossmember and the oil pan, it should be OK. The mileage is within a realistic range. They can go bad at any time, but the typical range is somewhere around 90-100k. There is some movement with these mounts. A fairly good way to judge the wear on mounts is to see if the engine fan (models through 1991) is not centered in the fan shroud. if the shroud is in good condition, the fan should be mostly centered. A fan that is touching the shroud is a clear indication of poor engine mounts. However, if so inclined, replace them and you are free and clear of doubt. But of course, that costs money. Good luck.