Faulty Ross Compressor clone - help please

[Timski]

Hello,
1st post here.

Whilst it's not a DIY stomp box I thought this would be a good place to look for some help.
I have a Barge Concepts RC3 compressor (high quality Ross clone). Barge Concepts unfortunately no longer exists and a few months ago the Sustain knob stopped working properly. It appears that, when turned, it no longer makes much difference to the sound and is stuck at a high sustain level which is no good for me. The pot itself is not loose.
Can anyone give me some pointers on how to investigate and remedy this? I am a complete novice when it comes to circuits and haven't wielded a soldering iron for about 20 years!

Thanks
Tim