The cracked Air Filter Bracket is common. If the engine is shaking you need to do what is needed to calm it down or it can happen again. I guess I lucked out with mine. My engine shook a lot but the mounts on the bracket loosened instead of it cracking.

Also from this forum there is a fix where you put a 3/4 or 1 inch ID section about 8 inches long of heater hose under the Air Filter Housing where it hangs over the Cylinder head/Valve Cover. That limits the distance it can vibrate.

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84 300D, 82 Volvo 244Gl Diesel