As for building optimal mass for the triceps, Compound exercises rule. Pushdowns and machines are really not giong to be the best option.
IMO, the best exercises for the triceps are:
Close grip BB Bench (flat/incline)
Floor Presses (DB/BB)
Also, skull crushers are a terrible exercise IMO if you are experiencing elbow pain, they put a ton of stress on the elbow joint and should really only be used if you have nice healthy elbows with good form.
So I would just throw out all of the isolation work for your triceps and just use DB's and BB's for a while making sure you have good form. It is easier to have pain in your elbows diong isolation exercises.
It would help out a lot if you could post your entire routine.