I have found the same thing, parts which are currently available are not made to the same (any?) quality standards. Does anyone know if synthetic corks are available?
If it's any consolation, the problem is even worse with classic cars. I have an MGB, for which there are a large number of suppliers offering literally everything, enough to build a new car. Whilst the prices are attractive, quality and durability are not. Replacement road springs for example appear to be made of poor grade steel which is not tempered properly, hence they very quickly lose their shape. The MG probably suffers more than most because there are so many still in existence making it an easy target for the supply of parts.