I could be wrong here, but this info comes from what I learnt when buying mine, also I don't know the official procedure, this just works for me.

That's a grease gun, not an oil gun (same one I have), so expect it to leak all over the place although newer ones with the cut threads rather than the cast work much better. Someone is selling alot of these old grease guns as "Myford" oil guns and they're just not.

Unscrew the cap, push the check valve down to the bottom of the chamber (the nozzle will extend out the front – or perhaps just pull the nozzle) and fill to the top leaving a small air gap (5mm?)

Applying some PTFE tape will help stop leakage and sure up old threads a bit! Tighten gently especially on the old cast thread version.

Ensure the small cup that mates with the oil nipple is smooth and free from rust or pitting or you'll find it sprays oil out sideways at some surprising velocity

there are also 2 different nozzle types (or so I believe) I've not seen the other type, but there is basically an old, and a new type – if you have the dicast threads, chances are you have the old nozzle too, suits my 1953 Myford just fine.

Edited By Russ B on 03/11/2014 13:46:16