TC3 shocks are not the easiset shock to get working right but once they are they are damn near as good as tamiya shocks, though they do need more regular maintance than tamiya shocks

first of all make sure the rubber o ring that goes on the threads under the cap is in good nick... its only about 10 bucks for a rebuild kit and it has all the o-rings in it... they should last ages... fill the shock with oil and move the piston up and down a few times to get all the air bubbles to the surface... then let it sit until they are gone... top up the shock and move the piston again... if there are no more air bubbles make sure the shock is full of oil... then fill the cap about half full with oil and quickly get them together, holding the shock on an angle of 20 or 30 degrees (doesn't have to be exact)... slowly screw the cap down and you'll hear the excess oil and air being pushed out... its a bit of a pain and it takes a bit of practice to get it right but when you do the shocks will be pretty close to perfect

hope it helps