I got a 4-20. It has been in use about three years now by myself and three buddies....hundreds, if not thousands of lbs of WW/pure lead/linotype smelted/cleaned and fluxed or melted and poured. It is used for making ingots and bullets.
I used to think it was dirt from raw wheel weights that clogged the nozzle. But think about it....any sand or impurities in the dirty lead is just vaporized, burned away or simply floated away as dross. Flux often using corn kernel sized pieces of candle, stir slowly but thorougly so that residue on the side and bottom are freed up to float.
Anyways, if the nozzle is stubbornly clogged, a paperclip will clear it easily.
It would leak sometimes when it was new, then I/we figured out that the melt temperature must be kept within a certain sweet range, between 6 and 6.5 on my thermostat. Perhaps a tiny nugget of lead that solidified could be preventing the needle valve from seating properly, hence the leak.
You should keep the melt temp hot enough kept the nozzle from clogging as well. When adding ingots, you have to give enough time for the pot to recover to its sweet temp range before pouring, otherwise lead will solidify in the spout. It is better to keep the melt at a high level...always close to the maximum capacity...so that adding 1 or 2 lb ingots will not change the melt temperature appreciably. As well, preheat ingots by placing them on the rim of the pot several minutes before adding to the melt.
Sometimes, to stop a leak or to increase melt flow, you may have to adjust the height of the needle by screwing it up or down as required.
Using the Lee melter successfully is a simple matter of using a little patience and a little technical common sense. Melting lead is not rocket science for gosh sakes.
I highly recommend the Lee 4-20 bottom pour pot.