Micro Seiki DDX1000 problems

Hi everyone.... :-)

After years of not having a turntable is my system, I made the decision to
re-visit my 1978 audio system, in particular my Micro Seiki DDX1000.
This time around the plan was to change some things and upgrade the Table
with some modern solutions for better sound. I mass loaded all the cavities with
with lead shots and potting epoxy, the inside of the turntable got layers of dynamat and more lead-shots and epoxy. The final result is truly remarkable
where the whole turntable used to ring and sound incredibly hollow, I now have a turntable that feels hewn from one solid inert piece of metal.

I added a Trans-Fi Terminator Tangential tone arm (what a fantastic piece of gear) making the DDX look very space age indeed.

Now to my problem....
I turned on the table, set the speed, dropped the needle on the record, everything was fine for a minute or so, but suddenly the speed shoot up
and then it was no good until I corrected the speed again :-(

I'm totally bummed as I spent a ton of time and money on this project.
Does someone have a solution to the issue I have

Thanks in advance.

Peter