Difficult to get back in?  I just loosen the bolt enough for the air to
get out, then when it starts spitting coolant, I just snug it back in
again.  No difficulty & cheaper than 20$.   malcolm

>  <<snip>> > It is a beautifully made petcock assembly that
> replaces the bolt "plug"  on the top of the radiator that is so
> difficult to get back in while coolant is coming out during system
> bleeding.