No, and Yes.
Actually it is a new Fluidmaster syphon and valve. No idea why I said it was the old inlet valve. Regrettably it's plastic, no brass fitting. (And it is a tight fit)
In order to replace a syphon diaphragm, on a toilet where the cistern 'sits' directly on the toilet basin rather than by plastic pipe, I've had to completely remove the cistern, which has involved disconnecting overflow and water supply too.
I cannot get a watertight seal again between the...