After 30+ years, you can safely assume that anything made out of rubber will need replacing unless, of course, replaced recently. All wear items do in fact wear out. The parts for a MB W123s are pretty cheap compared to newer cars. You can replace entire systems on the cheaps ... which is what I suggest. I never owned a gasser MB, so no clue about them except those parts in common with diesels. Do some market research on components, and pricing. The W123 is not everyone's cup of tea. I got hooked on the W123 back in 2008. Nearing the end of the project so to speak, so it's a hobby for some, other's a DD, and other's just a passing episode in car ownership.