Loricraft PRC3 could use some help

I have about a PRC3 of unknown age (5 years old to me)
and it needs some help I think. I just replaced the belt and that solved a couple of issues with the platter. I'm still experiencing a lot of thread pulling out while it's cleaning a some vibrations that are causing the arm to jump and vibrate periodically. Any suggestions? Is it vacuum pressure related? Do I just need to find a place to have it repaired or is there something I can do at home?
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My PRC3 arm is set with downforce at zero (ie, with the vacuum turned off, the arm floats level).

There's no need for any downforce. The vacuum alone is sufficient to keep the nozzle riding lightly on the record and sucking cleanly.

Additional downforce can cause thread "unwinding". Too much can even cause marking of the vinyl surface (visible in the flats between the runout grooves on a shiny record).
Ok. I'll try this. Thanks.
No perfect solution so far. I checked vacuum pressure and it seems good. I flushed the armtube with hot water and I decreased tracking pressure to zero. The only thing that does work is going back to the outside-in method of vacuuming which I guess isn't as good but the record sure looks clean.