Looking back over this thread, if the compressor is working at all on both channels then the problem is certain to be either one of the gain cells is faulty, or, more likely, that it has taken a knock and the relationship between the LEDs and the gain cells has been changed…. one of the gain cells has moved away from the LEDs.
It’s worth removing the plastic covers (on the gain cells); one plastic cover is over a single cell and LED, that one controls the compression meter.
The other cover is over 2 gain cells which are set close to the pair of orange LEDs (you will see when you get the cover off) The gain cells should be close to the LEDs , the closeness controls the amount of compression so compression imbalance can be corrected by moving the cells.
If you are sure you have a faulty cell, I can supply replacement gain cells as they are difficult to get. The price is $5.50 each plus $5 for shipping. (I need to confirm that shipping cost)
It’s worth giving the above a try as sending it back to the UK will take time and effort and shipping is expensive.
If you do decide to send it to me be sure to mark it clearly as being sent for repair otherwise we do get problems with customs.