Discussion about the Korg PolySix synthesizer

Hi,  this is my my first post to this group. I bought a Polysix
recently   realizing they're very old. Actually played guitar mainly
in the 80's but there was always a PSix in my basement studio.
Background: this unit had maintenance performed by Korg in the 80's
and the battery was lifted into a socket before any damage occurred.
It works pretty good except; I noticed some volume issues (not being
very responsive to cranking it up!) I believe I solved this issue by
working the volume pot a few times-maybe a scratchy pot in need of
cleaning. More importantly, there's an issue with the VCF cutoff. It
doesn't track well when at the lower freqs. When I move the knob it
sounds like it's dirty and cuts in and out. When it's stationary (not
moving) the freq cuts off where it should. Just to be clear, I can set
it any where and get the correct cutoff, it just takes some tweaking
at the lower end. This again sounds like maybe a dirty pot. I have
heard that the filter chip set may be going?? Not a tech head myself.
Sorry for being longwinded but I need to keep this dinosaur roaring!!
 Any feedback would be appreciated