Onetap wrote:

I went through this process some years ago; a complete waste of time,
with hindsight.

There were no standard sizes and the covers seem to have been sand
cast in small foundries.
Grouting in a new frame isn't a difficult job. Just buy a new pressed
steel job and resign yourself to installing a new frame as well.

Unfortunately it's like plumbing (and many other construction
disciplines)... Nothing old matches with anything new ;-)
You'd probably eventually find a replacement lid but it will be an original
and could take you weeks/months to source.

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