Trying to prevent feedback loop with stereo fader pair - help!

Hello folks,

I'm still at the early stages of finding my feet with MaxMSP.

I'm building a little utility device to help me with another job. It takes two mono inputs and gives me basic level, mute and (very basic) pan control).

Sometimes the pair of inputs will be dual mono, sometimes one stereo.

I've got it pretty much working how I want except for one thing:
In stereo mode, the left hand fader and mute control the right too - all good.

I'm not sure how to make it possible to control the left fader and mute without creating a feedback loop where both faders have outputs feeding the other one's input.

For clarity, I'm not talking about audio feedback, I'm talking about feeding the parameter value output of one fader into the input of the other. It works fine now with the left controlling the right, but I want to connect the right to the left also, so I can control from either fader.
I've tried various things with the change object, but it gets really messy and doesn't work.

Is there an elegant way to do this?
Patch attached (in very in-progress untidy state!)