Deuce:

I had a similar vibration in my 1987 300TD wagon after I purchased it.

About two months after persistent use of PS (double dose at every fill up) and some occasional use of other cleaners, the vibration was reduced both in term of amplitude and frequency. At that point, I got the vibration, maybe 1 out of 5 times (compared to 1 out 2 times when I bought it), when stopped at a light at idle.

Now it is four months after the persistent use of PS, the vibration is completely gone. I could not remember feeing it in the last month or so.

In these four months, I have used some additional cleaners but mainly PS. I have used one bottle of Techron and some Gunk diesel fuel conditioner. Also lately I have been using a Premium Diesel fuel from Crystal Flash.

My experience tells me that you might want to be patient and keep cleaning it up. In the mean time, also try to use some
oil that has lots of detergent in it (CH-4 rated), if you are not already using it.

I was thinking motor mounts all the way but cleaners did the job. It was not over night, but it did it. Originally I was preparing to change the mounts in the spring after the Michigan winter but now I am not going to tough them.