If you require parts, it's best that you locate them with an authorized Crown service centre. The t-sens foam is still a foam, with some sticky tape on one side. This is used to hold the thermal detector in place, on top of the tab on the last fet of the HS (high side).
It is possible that one of the channels could have been set offline because of a discovered fault. Locate the Front End boards, around middle of the BCA board. There is a green led that indicates that the FE card is in Ready mode and awaiting for signal. After a minute of silence, the Ready indiocator of the FE card should turn off, offline position. If levels are set, just touch the input connectors to restart the FE card. If all fails, try with signal; If still all fails then you may have an output issue.
Power down and discharge the caps (at the rail connector). Swap FE cards; Power up : If the issue changes place, then the FE card is at fault.
Power down and discharge the caps. Remove the gate drive cards; Check for diode measurement on each fet and flyback diodes; If you discover a fault, verify the gate drive card for damage; Do not power up amplifier with damaged gate drive cards! Either rebuild or replace the card;
Heat related issues could be caused by a lack of refurbishment or ULOL adjustment.
You may want to add a compressor : Since you mention that peaks are passing through, perhaps a compressor may control the peaks.
Please explain the statement Gain on Mixer set at 30dB; If this is true, it is possible, as Deromax stipulated, that the mixer is probably clipping, not just the amp.