Cameron, if you say "something's not quite right with it", I would be willing to guess your instinct is correct. Those Johnson Electric motors are not a quality motor, & are not made to be repaired.
Huskyvacs could very well be correct in his assumption that the vacuum was left outside on a hot day & this caused the damage to the filter cover that holds the pre-motor filter in place. However, I am willing to bet the more likely scenario is that this vacuum's original owner had the damage occur while using the vacuum, & realizing it would be a expensive repair, sold it to someone to make a quick buck & replace the TriStar with another vacuum.
You can use a Ametek double stage motor from the CXL in the CS. But, to do so, you need the motor mount from the EXL, the first model in this series that used the Electro Motor double stage motor, & that part is discontinued. What I would do is go on Ebay or find a EXL locally & transplant the motor & motor mount into your CS. Then, when that motor eventually fails, you have the mount to use your Ametek double stage motor. You will also benefit by being able to save certain parts that may be needed later for repairs. Yes, you could buy a new Johnson Electric motor, motor mount & filter cover or a used MG1 or MG2, but considering the Electro Motor used in the EXL is better quality, longer lasting & offers the same suction & airflow performance, I would personally upgrade to the EXL motor if I was in your position.
Best of luck getting the vacuum up & running again. Such a shame that a recent model, high end vacuum like that had a motor failure like that early on, but I'm sure you will have it in tip-top shape in no time at all
Rob