Selector detent plunger weak jumps out of third?

[Berridale]

Selespeed gearbox detent plunger weak?

This would apply to any Alfa gearbox.
Just guessing that the jumping out of 3rd gear is related to a detent plunger being damaged.
Started to strip the 147 Selespeed box and noticed this
The protrusion of the detent ball is less than the other, maybe 3mm.
There are three detent plungers on the side of the box , two are paired one of these has the ball that doesn't come all the way out.
Pretty sure it is the upper one.

Anyone been down this path?