Easy to replace that belt set, though you will need a screwdriver with a JIS tip to undo those 2 stuck down screws holding the capstan base bearing. After that the rest of the rubber parts looks in good condition, so they will run for a while longer before you have to replace them. Might still all be available from Sony as spares or as a kit, though you will pay for it. The kit however does include the felting pads for the take up spool clutch, which does wear.
I have some later versions somewhere........
That manual funny enough is not atypical of older 1980's and 1990's eastern made equipment, I bought manuals ( yes actual paper manuals with either 3 colour print or full colour Pantone images inside, often with a fold out A2 circuit diagram in 4 colours inside the middle, and often with multiple colour pages or detailed exploded diagrams of assembly and service instructions) for things like TV sets, VCR's, cassette decks, CD players, radios and even washing machines.
The quality of the manuals was very good, but as the manufacturers moved away from quality to cheap junk the manuals dropped both in detail and in quality, often they now are barely more than a copy of the instruction booklet ( often only a poor copy as well) and a block diagram, with the fault finding going down a tree to "change XXX board" at best, and barely a diagram of how it goes together.
The old manuals from Goldstar, JVC, Aiwa, Technics and Matsushita were often very well made works of art.