I cannot imagine that WD-40 would do any more than make an already shiny and slippery platen even more shiny and slippery.  Be aware that there is a lot of nonsense about typewriters on the internet !

I would not consider using WD-40 because its pungent smell does not seem to go away.

And I do not loose sleep over hard platens.

I use a sheet of this Avery product as a backing-sheet for my typewriter paper.

I cut it to the same size of my typing paper...placing the soft plastic directly in contact with  my typing paper.  And leave the peel & stick backing paper on the sheet of laminating plastic on the Avery sheet and that is against the old platen rubber.

After a month or so of use, you can see all the indentations of the type-slugs in the plastic  of the laminating sheet, throuw it away, and I just grab a new, fresh sheet to start the new month.

These plastic laminating sheets give the type-slugs some soft plastic to impact and it also makes the type-slug much more quiet as I type.
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Pete E. wrote:

I would not consider using WD-40 because its pungent smell does not seem to go away.
... snip ...

There are more and better reasons than the smell not to put WD-40 on a platen.... Honestly, it sometimes feels like WD-40 is defining the 21st Century!

M. Höhne wrote:

There are more and better reasons than the smell not to put WD-40 on a platen.... Honestly, it sometimes feels like WD-40 is defining the 21st Century!

I did the test with one of my platen, it spent 4 days in a bath of WD-40, and it work. The smell longer contains rubber and oil, original smell, than WD-40 ...
This seems to work well, because the rubber is more flexible (but not softened) and it sticks much better !
Obviously, this does not replace re-surfacing, but it definitely helps !!!