[Arran]

It looks to me like the underside of the chassis is unmolested so I think you could probably work without a schematic by replacing one part at a time. The only part that you would need service info for is the alignment data, which you would not need either if the dial tracks properly across all bands.
Permeable adjusted IF cans and coils don't tend to drift as much, at least ones with proper fixed mica caps not those cheap sliver mica ones used in K-tran style mini IF cans. I do see a mica sandwich type capacitor under the chassis so it would be best to check any of those, that style of construction has a high failure rate, not so much for leakage but for drifting in value.
Yugoslavia was kind of an oddball country as I understand it, it was a dictatorship, at least a nominally Communist one, but they actually had better relations with Western governments then they did with Moscow. Unlike Poland or Czechoslovakia they were not in the Warsaw Pact nor were they a Soviet satellite state. I noticed that this set uses Swedish made paper capacitors, the resistors look almost like American/Canadian made carbon composition types so those may have been imported as well.
Regards
Arran