LNAV problems

As I posted a few months ago, my LNAV was having problems (crazy g-
meter and averager readings) and Cambridge could find nothing wrong
with it, plus after their first try they stopped servicing LNAV's. I
then purchased a used LNAV from someone who contacted me from my post
and for a while that worked fine, but on a recent flight it too was
acting crazy, but in a different way.

It read 1200 feet high when the altimeter was properly set, the
altitude required was independent of the distance to the goal (and of
course therefore wrong), and the McCready setting jumped from 0 to 3.7
to 7.4 to 9.5 and then (when decreased) jumped down in 3.7 increments
to 5.8, 2.1 and 0. (It seems to saturate at 9.5 and 0.) It also was
telling me to push the whole flight even though the vario was reading
correctly. On my next flight, this erratic behavior was not present.

All of this leads to two questions:

1. While I could have two LNAV failures in close proximity in time, a
more likely hypothesis is that there is a wiring fault or electrical
noise or something else causing both units to either fail or seem to
fail. Does anyone have any experience here?

2. When I posted about my original LNAV's problems in March, Paul
Remde indicated that Cambridge was in the process of solving it's
problems and I might be able to get LNAV service there again. Any news
on that?

Thanks very much.

Martin