Krell KSA 250 – rustling on one channel

Hi,

I bought one of these beasts on the used market from a store and from the day it arrived at my home, the left channel is causing me grief: from time to time, there would be like disconnections on it in the form of rustlings that would either be audible from my listening spot and/or cause the sound on the left channel to decrease and the whole soundstage to shift rightwards.
this could be happening a couple times an evening or sometimes once every other day. when it happens, i disconnect and reconnect either the HP cable or the interconnect and the problem usually disappears.
It’s less likely to happen if I first let the amp warm up before playing music and it’s more likely to happen while playing music in low volume.
I live in Paris and service for those amps here is basically inexistent and if existent, it’s not very reliable and extremely expensive. Other than that the entire Krell support in France is doubtful (they don't even answer emails).

any ideas where this problem could be coming from?

how would that be resolved and how much it should cost?

any recommended Krell service centres in Europe?

Thanks for your help.