Varicalc Audiovario Problem

I've sent this to the guy who designed and built my Varicalc 2 vario,
but thought that posting here my get a fast response. The Varicalc 2
was built in 1990-ish and has audio, Speed-to-fly and Final Glide.

Two weeks ago (last time I flew my ship), the audio was working
fine... well, except that the TE wasn't working properly, so I got
"stick thermals". I have since replaced the TE tubing, T'd the TE
below the seat (as far back as I could reach) and tested everything to
be airtight.

I turned on the Varicalc and it did it's normal startup screen,
started high and dropped back to zero (all normal). Then it continued
to drop... down to -6.7 kts and stayed there. Tried it later last
night, it stabilised at -4 kts. This morning it went to -8 kts. This
occurs while sitting in the workshop, sitting up on blocks, regardless
of connecting the pneumatic lines or not -- so I don't think the
problem is in the tubing.

The mechanical vario shows correctly, even with switching the TE
tubing (in case one was pinched). Further, if I apply a slight
pressure or vaccuum at the TE port, both varios respond and then
settle back to baseline (unfortunately the nasty negative for the
Varicalc).

Any ideas? Suggestions? I'd really rather not need to replace my
Varicalc.

John