It is a definite frustration. Shouldn't be this hard to put together decent rubber bits nowadays, but I do understand that we're a tiny market.
A couple years ago I wanted to replace the heater valve on my Morris. I looked at the UK supplier and in their description of the part they said, right upfront, don't buy this, it's crap.
They eventually found a better supplier, but I had to chuckle at the honesty.