Vintage Synth Repair

I've got a new (to me) MKS-80 Super Jupiter that seems to be working 
at about 75% right now. The upper voice board has a problem with 
voice C's PWM, on both VCO's, that I've traced to a bad inverting 
input on a TL064CN. There's audible PWM that looks like a negative-
going DC ramp on the scope (measured at the opamp input, and directly 
out of the S/H on all four channels). The output of the opamp is 
wired directly to the inverting input of that opamp, which should 
cause a phase cancellation. Since the inverting input is not working, 
I wind up with audible modulation on the PW at higher PW settings.

The lower voice board is also missing PW control on voice C. The 
culprit there looks to be the 4051, as far as I can tell. If I jumper 
the voice D PWM output of the S/H to voice C's output, I regain 
control over voice C's PWM. That leads me to believe that the opamp 
path on this board is good, and the S/H is bad.

Here's the question - the MKS-80 voice board design holds four voices 
on a single board, which all share common parameters. Since the PWM 
setting for all VCO's is the same reference voltage from the DAC 
(albeit fed into separate channels of the 4051), is there any reason 
why I couldn't simply tack a jumper onto another output channel of 
the 4051 that sources PWM for this board and feed the separate opamp 
stages from that? Each VCO has a trim pot for PW offset, so assuming 
that I'm not too close to either extreme, I should be able to 
calibrate the PW on both voices.

I'd prefer to swap the IC, as I'm going to do on the upper board, but 
it's nice to have a backup in case the proper IC takes too long to 
find.

Thanks,
Adam