Listen to Andy B!
To get a genuine VX part that will last you buy from VX. If you want a cheaper clone aftermarket one then buy it from anywhere else.
Here is my tale of woe that might be of help in your decision! Firstly I live in an area where the roads are poor to say the least. Leicester City Council is renowned for punishing of the motorist in every way it can! After a mot advisory that the ns one was showing its age I opted to change them both because the originals had been on for 150000 miles from new.
I bought a wishbone from VX and a second some weeks later from a Motor Factor of good repute (or so they say). I did that because money was tight at the time (I had just paid my council tax) The VX one is still going strong after 10+K while the clone I had to change again after a few thousand when the ball joint failed and started to clunk. They were in different sealed plastic bags too, the VX one was made in Germany and in a GM labelled bag, the clone came in a nondescript bag with only the part number on it. The difference in cost was about 20 quids or so.
Says it all I think.
GudLuk
the industry wide advice is to change wishbones, or any suspension parts, in pairs. To be specific, a pair that are the same as each other, not an odd pair, hence not a pair at all.
ps listen to B if you want, but you wont find wishbones in a supermarket.

(wtf?

)
the point of my original post was that there have been numerous early failures with various "cheap makes" of wishbones, as you have clearly dicovered. Lemforder are, to my knowledge, the most reliable supplier, mostly because they supply them to gm!....and can be had from a factors for £110 a pair, as apposed to £460 a pair PLUS VAT FROM VX for the exact same part. Yes you can buy cheaper bones but odds are the job will need doing again soon, mainly because nobody in their right mind is going to stand up on here and guarantee a £50 pair of wishbones are going to last more than 3 months never mind 3 years, again, for reasons you have discovered.