The SL-C can generate very-high suspension loads which can cause the stock ball joints to wear out quicker than you'd normally expect. In fact, one builder noticed much For this reason, I decided to upgrade all four lower ball joints. The fronts are race-grade ones manufactured by QA1 and the rears are stock because the QA1s won't clear the the rims. The ones from QA1 have the following advantages over the stock ones; they're heavier duty, completely rebuildable, and have an adjustable pre-load.
QA1's rebuildable ball joint; screw-in housing shown, I have the the bolt-in housing
“I liked the concept that they were rebuildable, but I wasn’t expecting to rebuild them before they were installed!”
Custom aluminum 0.25" ball joint spacers
I bought model 1219-103 and discovered that the stud was 1/2" too short. Because they are rebuidable, this was easily fixed by buying the 9029-203 ball stud and installing it (note that I should have bought 1210-203B which comes with the appropriate length stud). My friend Will also figured out that everything was off by 0.25" so he designed a custom spacer, I 3D printed a test for him and then he had several sets water jet cut out of aluminum. This is what they looked like after a little sanding.
The top of the ball is 0.25" closer to the ground which will lower the roll height a little which doesn't seem like it will hurt anything.
Setting the pre-load or rebuilding the ball joint requires custom tools which are demonstrated in the video below.