I can't speak to the durability of the Lemforder control arms (their tie-rod ends are working well on my Porsche 944), but over 5 years/102K kms my Meyle HD control arms served me well on my 325i. The reason I chose them was that they use a full metal ball socket with a larger ball joint than stock. The reason for the failure of the OEM ball joints is that they actually have a rubber surround between the ball joint body and the shell that breaks down and causes play, that then causes the ball joint to fail.
Well, that's according to the reason given by Meyle on their website for their re-engineered HD parts---check out their website http://www.meyle.com/EN/Service/Down...formation.html
and go to page 9 dated 2004/12 'Control Arm (full metal version)". There you can download a PDF on the product and at the top of the page is part numbers for just the ball joints or an entire control arm assembly, and even a pair of control arms.
Hopefully this helps. I started to get a slight vibration in my front end on certain small sharp bumps that I though may have been a ball joint going, but it turned out to be the left front stabilizer bar bushing had play in it when you hit the stab. bar with your hand---the rest of the suspension was tight. I also recommend looking at their rear strut mounts; page 11 dated 2002/09 "Strut Mount". I had them in for 120K kms---I checked their condition when I removed the rear shocks (I was parting the car out) and they were in excellent shape.