Revox C279 subtle crackling.

Hello fellow audiophiles, I got hands on a revox c279 in quite good aesthetic condition at a very good price... Unfortunately it has a low level, random crackling sound in the left master channel. It comes and goes but it's audible. The first green led in the Vu meter lights up when this happens..It's not very invasive but it makes me feeling uneasy about my purchase.
If fixable, I'm not planning to return it...

Is this something I can fix by cleaning or probably some condenser needs changing?

If that was the case... How can I locate it?

Being an old desk and all, is it worth going the full recapping way? (Self made out profesional)

What would you do?

Thank you!
Could be a failing resistor, capacitor, transistor/IC, dry solder joint... A cool-spray is one way to debug this, as is an insulated prodding stick (plastic chopstick works well) - usually the faulty device will respond obviously to thermal or (gentle!) mechanical disturbance.

I presume you've tried moving all the controls and none are directly correlated with the noise? Try turning down all but one channel and see if its related to which channel is active, as it might be being injected on the mixing busses rather than internal to the masters.

How old is it - caps should last a few decades. It may be quite hard to work on, I'd say don't jump into massive amounts of rework without cause.
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