Most race cars don't drive in rain, snow, salt, etc... and if they do they swap them out frequently. These seals will help that problem.
http://www.speedwaymotors.com/Seals-It-Heim-Seals,1528.html
Second issue with heims is mounting them. A heim on an OEM knuckle is probably mounted in single sheer. While bolts aren't designed for this type of load, a .675 or .750 grade 8 bolt is typically of sufficient strength to handle it. The issue comes from the tolerance of the hole drilled in the knuckle, which is certainly not good. No matter how tight the fastener as the load cycles back and forth the softest materal starts to wallow out.
OEM gets around this with a tapered fit... the tighter the nut, the closer tolerance the hole to the fastener (TRE in this case.) If you have ever seen a d44 high steer arm mounted they use the tapered washers for the same reason.
There is a pretty cool solution for this if you have no other way than single sheer and you don't want TRE's. It's GM taper so your going to be reaming anyway.
http://www.speedwaymotors.com/Adjustable-Tie-Rod-Adapter-Stud-to-Heim,3333.html
The other solution is to somehow capture the heim between another mounting tab. This will make much less of a bending load, and limit the deformation of the knuckle hole.