wrote:
I am aware that they needed to stay balanced to prevent flutter... but I'd heard that just as an
overriding rule, moveable control surfaces are unrepairable.

I looked through my Cherokee service manual as an example. It doesn't specifically forbid control surface
repair, but it seems to imply that it's allowable... so long as it's within the balance limits. In fact, it says,

"Where possible the control surfaces were set with the balance weight on the heavy side of the limits, to
permit limited repair or paint touch-up without adjusting the balance weight."

and
"All replacement control surfaces, or surfaces that have been repainted or repaired, should be rebalanced
according to the procedures given in Paragraphs...blah,blah"

Seems that at least in the case of a Cherokee it's OK... provided they stay within balance limits.

BTW: Paint shops are specificlly certificated by the FAA because of the
possibility of getting controls out of balance. I know of no paint shop
that paints control surfaces without removing the surface first and
balancing it afterwards in any aircraft.

I had a truck back into my Mooney's aileron in Mexico. When I got it
back to the U.S. the Mooney Service Center said that, although they
could reskin and repair the damage they didn't think I'd ever be happy
with the results. They said they've never seen a repaired surface fly
straight. As a result we bought the $2300 new aileron from Mooney. Now
I'm sure some people in the back woods bend their control surfaces back
and are happy with them but other pilots are pretty picky and the
Service Center needs to accomidate that.
Some people drive Fords and are happy bending metal and others drive
Caddys and expect a certain "ride.

-Robert