It is far better to keep the radio stock than to mod it, like you've shown you'd like to do with it.
Schottky versus OEM?
Schottky is a type of diode, has only 1 junction (usually N) versus PN types - so the voltage drop across it is less - which usually means less drop - more efficient. Votlage Drop ranges from 0.2 to 0.4 (max.)
OEM - standard Silicon uses PN junctions and have a forward voltage drop of about 0.7V
OEM - Standard Germanium uses PN junctions and have a forward Voltage Drop of about 0.3V.
Similar to Schottky but were designed years - decades ago.
It is a personal choice on Germanium versus Schottky - any radio can benefit from the upgrade - but is it worth the cost? In some cases - age before beauty - also accounts for the audio quality and performance - so a personal choice. You said it was mint condition - so I can only wonder why the need to upgrade when you haven't even used it in the first place? I can understand car tires but not glass sealed envelope diodes that HAVEN'T had much use - you did not tell us if this radio has even been powered up recently.
Unlock Clarifier - Yes, by all means - done right though. 6kHz slide? Do the simple conversion of unlocking it first and use it that way for a while else only if needed to have done - a lot of this deals with current draw across parts like the Voice Lock control - that; as they age, can get tricky to operate due to bad spots and dirt in the chamber that houses the wiper arm and composition. So it may not work "linearly" and can jump - a good cleaning first and simply jumpering (relocate voltage source to a constant versus switched and breaking a switched line D56/D72 TX stuff) the Voice Lock Pot to the same Voltage power feed the PLL and don't change any resistor if you can, it's is not necessary and if done like I said, the drift is less and you have more than enough slide for most QSO's (conversations).
Receiver upgrade? Look thru this thread...
https://www.worldwidedx.com/threads/how-to-perform-the-2sc2999-and-schottky-diode-swap.23680/
The thread is long but look thru it to see if it's something you want...
Because below is a partial schematic of what you have in the radio - and so review their conversion procedures listed in that thread before you have this done. It's marginal improvements - and Schottky would take on most of the issues and give you potentially a better, quieter receive than to upgrade the RF amp and front end.
Now, you may not care to understand the above, but you are asking for opinions. Because if you don't know what is IN the radio - they can do some simple stuff and SOAK YOU for their falsehood.
It would be a wise idea to protect yourself and take photos - camera or phone (use MACRO setting for Focus) and open that radio case and take pics, for that may be your only defense against fraud.
Because, a lot of that radio uses parts that are not on store shelves and commonly found - it's more extinct than proprietary these days.
The PIN front end protection is one area that has a particular type of performance curve that makes this radio what it is. The RF amp? Many would say just keep it - others would say try the 2SC2999 - READ THE LINK ABOVE for that... then decide SCHOTTKY is included in the thread - I recommend you read it.
:+> Andy <+:
