Rotel RB970 BX Mk II crackly output from right channel

My Rotel RB970 BX mk II has been in use for 20+ years now and has recently developed a crackle on the right channel even when no input is being sent from the pre-amp. A long while ago I did open it up for a general dust and noticed some corrosion (or leaking?) around where the four big capacitors sit on the board. I'll try to dig out those pictures.
Any thoughts on what has suddenly caused the crackle to develop?
Is it likely to be terminal?
Thanks!
 
These were taken Dec 2021...

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