I am not that mechanically minded so i can only report on the symptoms my 318 had. It all started with a slight rattle at idle in park. After a few more evenings out in her ( no more than 40 miles) it started to get louder. Shortly after on my way home one morning a vibration started and got progressivly worse. I was so close to home that i carried on. She got me to my door but it was bananaramed

When i took the box to Blue we opened it up and it was full of alley filings. The impeller had obviously come appart to some degree causing the rattle and as it started to disintegrate the verter lost its balance causing the vibration. Blue reconditioned the box and sent the verter away to be re built.It is put on a lathe and cut open, recon`d, then welded up and balanced.
Not sure if this will help you but i hope you get sorted soon
Phil