Fortunately rubber is not a “black art”.
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All of the above is easily done by reputable rubber component manufacturers and their products will last.
It’s the cheap, nasty manufacturers trying to make a a product without consideration of quality.

The best you can do is report it the where you bought it so they no longer buy from that supplier.

You are right. These parts can be made well.
I am still reusing MOWOG marked rubber on ball joints and tie-rod ends, etc.
It is sometimes hard to remember where you bought a particular part. I mostly use one supplier but at the present, with supply problems, you have to shop around to find the parts in stock.
And it is worrying when parts turn up loose in a ziplock bag and not in a branded container, although a brand name is not always a guarantee of quality anymore either.

A lot of rubber items are now available from Japan. They are more expensive, but a much better quality product.

Are there any sites that specialise in Japanese made parts, or do you have to search for each item?

Are there any sites that specialise in Japanese made parts, or do you have to search for each item?