[Whaam68]

I once fixed a Leak Stereo 70 which is very similar and the diodes connected to the output transistors needed replacing on the dead channel but so did the output transistors on mine. The equivalent replacement parts were fairly cheap and the horse shoe style pre set pots are definitely mechanically suspect due to age. It looks like you’ve done some of the caps on the faulty board so if it were me AND you are totally happy the output transistors are ok, I’d consider shot gun replacement of all the pre set pots, the small signal transistors on the faulty channels board and probably those diodes. There aren’t that many to replace. The resistors if carbon film and not obviously physically damaged are probably fine but worth checking values against the circuit diagram values anyway. Do them all on the duff channel board though before powering up on a lamp limiter. Also re clean the edge connectors and check for bent pins and any solder bridges (I’ve been caught out there before). I also used a dab of conductive grease on the edge connector pads but that was probably overkill. If you aren’t that savvy (like me) it may in the end be quicker than trying to find the fault by elimination. At least the removable cards make this era of Leak easy to work on. I usually get to the stage of losing the will to live then suddenly figuring it out. Good luck.