Palindrome sez:

Hence why I wrote "series switching element" rather than FET. If the
designer was brought up designing using pnp/npn transistors, he may have
always protected them this way.

Interesting you mention this... the silkscreen for the FET says "b-e-c".
Seems that the original design was for BJT, but component specs were changed
to include FET sometime in production with little regard for the confusion it
would cause service personnel who saw these markings...

Does this shed any different light on the choice of zener for this purpose?
And the possibility for a different replacement part? The 47v, 2W part is
looking like unobtanium...

Thanks,
--
John English