I am using a Terra mode "C" encoder which was installed
in my aircraft when I bought it 5 years ago.  During
the past 5 years it has failed 3 times.  The failure mode
is always the same, it mis-reports my altitude too low by
an increasing margin as I climb.  The last time it happened
was just after takeoff in IMC.  It got ATCs attention quickly,
and they had me squawk mode "A" only for the rest of the
flight.

Needless to say, I’ve had it with Terra.  Questions:

Has anyone else had this problem?  

I have a Narco transponder, and am condsidering a Narco
encoder to replace the Terra.  Does anyone have experience
to share with these?  

How about alternatives?  I saw an inexpensive encoder in
the Chief Aircraft catalog, but I hesitate to cheap out
on this ($150 vs $190).

Do all encoders use a standard connector, or am I in for a
major rewiring to replace the unit with another brand?

Thanks in advance for the input,
Mike Friedman, WB2WNX
Comm Glider
Inst Pvt ASEL
PA-28-160 N5504W "The Hershey Warrior"