Your service advisor is not BSing you.

Yes, engine mounts generally wear by "compaction", not by losing actual material. Losing material means that friction wear would have to take place. That's not the case with engine mounts.

Remember, the engine is sitting on the frame directly on the two mounts on the sides. The torque of the motor, turning clockwise (i.e. rotating slightly toward the passenger side of the car on the mounts) and then returning back to normal position, tends to compress and sag the mounts after many 10s of thousands of compressions. It's a fact of life.

In addition, any rubber part on the car is going to show wear after as few as 3-5 years. At 10 years, most rubber parts are junk whether they have been used or not. That goes for tires, hoses, seals, motor mounts, brake lines, whatever. All rubber should be replaced whether it looks or feels like it should be, or not. The ozone and natural breakdown, not to mention the extreme heat, chemical combustion by-products, and 600+ pound weight of the engine, in the harsh engine-bay environment, can and will do any motor mount in.

I have a 300SEL 6.3 from 1969, with just 56,000 original miles on it, on which I just recently replaced the engine mounts. They were quite worn!

Cheers,
Gerry