Our gate fell off the wall and I have now had it repaired by a welder,
who replaced the corroded steel post in its entirety. The gate is
perfectly level but the bolt is tight due to previous mislignment. It
may bed in with time.

However, if I want to replace the bolt what should I use? What is the
difference between a slide bolt and a barrel bolt? Can any type of
bolt be welded (by the welder) or is a particular design needed? Is
it worth paying extra for marine grade stainless steel given that the
cost of the bolt will will be insignificant compared to the labour?