Argon is an inert gas and non flammable.
Oil would not have caused an explosin with argon. Oxygen on the other hand...yeah....basicly with
oil in an oxygen regulator you have created a small deisel engine hanging on the side of a bottle.
Probably the spring had coroded a little in the regulator and when you hit it with 1400 psi from the bottle it broke. Sending 1400 psi into the low side valveing. Before you fire back up you might want to check your low side hose going into your welder...could have blown that off or up when it all failed. Also check your solenoid valve on your welder.
I never stand in front of a regulator when I turn a bottle on. I have seen the stem shoot out of an oxygen regulator before and punch a hole right thru the shop wall. Scary stuff.
I dont rent my bottles. Buy the bottle outright. You pay more up front but then its just gas charge after that. I dont know what size my bottle of argon is but the bottles about 4' tall +/-. When i get it exchanged it runs me about 30 dollars because i own the bottle.
Gene