Land Rover series gearbox layshaft - replace ?

Ouch. That’s the result of ham-fistedness. Someone’s been in the habit of slinging it into reverse either while it’s still rolling forward, or wth the revs high prior to dipping the clutch, so the layshaft was still spinning as they tried to get the gears in mesh.

It sort of depends what else he’s doing while he’s in the box, and how he’s going to treat it once it’s done.

If he’s got a good/useable replacement reverse gear and detent springs, is planning on reusing all the existing bearings and other serviceable parts, and is just throwing it back together with a new set of gaskets and seals, then it’d be fine. Noisy, and a potential future problem, but fine in the short/medium term. Driven with sympathy it would probably last a very long time; you don’t go that quick, or for very long, in reverse after all. If you know reverse is a little weak, then you’re not going to be putting it under any unnecessary strain either.

If, however, he’s putting in new gears and bearings and spending proper money on other bits, then I’d say it would be a false economy not to replace this too.

From what you describe though, it sounds like a bit of a “patch it up for minimal money” job, and that he’d be happy with a gearbox good for a few thousand miles of sensible use, rather than spending a load of cash doing a proper rebuild on something that’s seldom going to see much use. In which case, yes, reuse it.