Hi PWH
I wish I could help you here, but as Martin already pointed out, there is a discrepancy in the Service Manual.
Can you remove the diode, and try (with a magnifying glass), to see if there are any numbers or letters readable on the diode.
Before you remove it, make sure that you mark the polarity of the diode on the PCB - the cathode is a black ring around the glass tube, and I usually mark the cathode end with a black Permanent Marker on the PCB.
One thing for sure, is that all the other Purple (cathode-side) and Orange diodes on your PCB are 1N4148's. So, if it resembles one of those, it is probably a 1N4148. BUT, if it has a clearly identifiable Black ring, then it's probably a Zener.
Pls note - the color coding I mentioned above is NOT applicable universally today, and today almost all glass-diodes today look the same (Orange with a Black ring), irrespective of type. They will have some imprint of tiny numbers on them to denote the diode type.
Let us know what you can deduce - I have plenty of either of the possible diode types in stock.
Menahem
Learn from the mistakes of others - you'll not live long enough to make them all yourself!