Hello and welcome to the forums.
As far as I know these sets used OC series transistors.
I'd start by applying Servisol to all the pots and switches.
I'm not normally one to advocate wholesale component replacements, but those red/yellow/black Plessey electrolytic capacitors are unreliable.
The correct approach is to measure voltages and compare them with the service sheet.
http://www.service-data.com/product.php/655/1065/m10655