The standard shock that comes with the kit, and with several other cars is known as the VCS shock. There are also several alternatives, one of which is the CRC Durashock. The VCS and Durashocks are compared in the pictures below.
There is nothing particularly wrong with the VCS shock. Some people use the Durashock for the reasons that it leaks less, and that it is less likely to pull apart in a big accident.
Whichever shock is used, check the end of the shock shaft to see if it is flat. If not, file it until it is. This will make the shock end fit straight, which can be a problem otherwise.
For the VCS shock, use the kit shock oil which is 30wt. The action of a Durashock is different, so use 20wt oil in this to get the same damping. Soak the small black sponge in the shock oil before fitting, making sure the oil has thoroughly impregnated it. Also cover all the parts that fit onto the shaft in shock oil before fitting them. When filling the actual shock body with oil, it needs to go about 3/4 of the way to the top.
Besides this, follow the instructions for the shock you are building and you should have a perfect shock.
The length of the shock is important as this controls the amount the back of the pod will droop when the shock is fully extended. Adjust the shock length by screwing the ball cups in or out until the pod droops by about 1.5-2mm when the shock is fully extended. Cut the ball cups slightly shorter if necessary, but if this is needed at all it shouldn’t be much.
Fit the olive spring provided in the kit onto the shock. No other should be needed if the car is an L4.
