G'day hdon
These images, again, are way-too-small.

This must be frustrating for you!
Your images are tiny. I cannot see any detail.

Now, Nylock nuts are universally available and should be replaced.
I'm not sure about the adjuster pad.

Quote
The mower cuts quite well but the blade clearance is uneven.
That's a clue here. It means there is serviceable life on
the bottom blade [bedknife] but the surfaces are uneven.

Again, we need clear images of an internet size.

A Note on Back-lapping: -
Back-lapping can restore a well-maintained reel and blade,
but it cannot perform miracles.

But there is another issue for the Diplomat models ...
Back-lapping requires the reel to be rotated in reverse.
Here, a Left Hand thread on the reel pulley makes this impossible.
[the pulley would unscrew].

Please keep us informed.
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Jack