On the subject of TMH's, replacement was a Field or Base repair. The TMH part number was 'blocked' against a unit demand. I often wondered why as it wasn't a special time consuming fitting job but Ian Kxxxxx at REME Tech Services (later 14 MAG) told me that it was to save on costs. Being an expensive part - I seem to think that the last VAOS price was £91 or so - it meant that Field workshops would only keep a couple in stock on an as-need basis. If a rifle was ZF at Field or Base (you can only ZF a weapon at that level.....) they'd occasionally change out a perfect TMH and send it for the chop with an unserviceable one. That's presumably what's happened to yours with a re-number, to save an expensive waste.

Thinking out aloud, I'm trying to think of reasons for scrapping TMH's. There were a few faults.
Loss of the little front filler plate that was a simple repair. That was usually caused by letting the hammer fly forwards uncontrolled while the TMH is off the body.
Loose rear block that we could repair/tighten by dollying the cross rivets with the ball-pein hammer.
Worn out axis pin holes - virtually to the point of being oval! There was a set of ring punches to 'cure' this but ring punching really is a palliative and not a cure in engineering circles. There were several good suggestions to cure them*.
Never encountered worn trigger/hammer axis pin holes
Damaged threads in backsight housing slide part. Quite how was never explained to anyones satisfaction! Other bits easily rectified.

Got any more Tankie, Skippy, Son, BAR, BinO? Anyway, that's my Saturday morning contribution on this pommy Bank Holiday weekend

* The best(?) being a suggestion by the Armourer apprentices section at Stirling Base Workshop. It was a kit of two bushes that were bushed into both opposite overbored axis holes in worn out TMH. Holes then slightly countersunk internally. Bushes locktited and flared out on the inside to retain them tight. New two part longer axis pin and screw. VERY good but barely economic so I was told! They were well rewarded though for the time and effort. More to it than that of course and Bordon EMER team raised a few small points - if anyones really interested......