Vintage Synth Repair

hey guys, 

i've fixed both the modulation inputs for the filter and my noise
generator on my arp odyssey mk1 by replacing op amps. it's sample and
hold mixer doesn't modulate anything and i'm wondering if anyone has
an experience with this part of the synth. i've replaced op amp A2 and
the transistor Q3. One thing I haven't replaced is A3 which is a
unique part that i couldn't find for under $15! I noticed there was
mentioned of "Z3" working with a charge in C7, but i cannot find Z3
anywhere. 

do you think there are more op amps that i need to replace that are
feeding the signals INTO the S+H mixer or do you think there are op
amps that are suppose to be amplifying the output of the S+H... or
something else entirely?

thanks guys!
-johnny