I bought a couple of Auto tapping heads at a recent industrial auction. They are a fairly modern A STM JSN 12 and a older Archer No.1 with a No.10 chuck. The STM is a little big for what I do and is missing the reaction arm and metalastic collet. Seem to be OK but I’ll leave it until have a need for its capacity.
So the Archer:

The gearbox seems OK, but the friction clutch in the chuck wasn’t releasing.  Gentle  application of force with a bar wouldn’t move the adjusting ring. So as it hadn’t been abused before it seemed a good excuse to buy a set of flat C spanners. The forged ones I have are too thick to fit in the gap. So I bought these https://www.ebay.co.uk/itm/336402449654 They cost nearly as much as the tapping head.
Backing off the ring allowed the clutch to slip. It was however very rough. Taking it apart soon revealed the cause:

Clearly damp has got in there and rusted the plates. It’s also damaged the 3 vulcanised fibre friction discs. I’ll have a go with Evaporust to start with and see how that does.

Robert.