A Lieberman wrote:

I take it to the new place (where I had it done 2 years ago) and they said
my transponder altitude encoder was off, and could not be adjusted, either
needs an overhaul or replacement, altimeter needs adjustment and overhaul.


Older encoders (especially certain manufacturers) have good days and bad
days. Oddly, I'm still using the same ancient TransCal that came with
my airplane (I thin this and the ASI is the only piece of original
instrumetnation I have) and it's still going strong. My altimeter
was progressively wonky at higher altitudes until one money hungry
FBO ripped me off for a new one (and oddly the core, which I got no
credit for disappeared). Particularly galling in that incident was
that they quoted me a price to pull everything out and bench test it
(which I've never had any other shop do). After the altimeter failed
they wanted an additional $200 to put the new one in. I figured if
the thing was on the bench already in the initial estimate, the only
thing additional that needed to be done an extra line in the log book
(which generally is covered when you pay list price for things).
The only thing that I can say is that I've dissed these guys baddly
enough in local forums (along with the local traffic reporting plane
company owner) that we've taken a good chunk of their business away.