Guilliman found himself in a difficult position as he faced Evelyn's request.
Although the Men of Iron were not currently hostile to the Imperium, they were not cooperating with it either. They would only consider the agreement binding once they received the Emperor's diary. As things stood, even Guilliman did not dare ask anything of Iax.
After all, unbound by any agreement, the Men of Iron had already forced their way into the Imperial Palace once.
Guilliman dared not imagine what might happen if he handled this poorly. Next time, they might not simply force their way into the Imperial Palace, but erase it outright.
According to secret reports from the Inquisition, the Fabricator-General of Mars and the entire Adeptus Mechanicus had been unsettled lately, their ranks rife with arguments and factional struggles. Some Mechanicus factions were even secretly planning to defect to the Men of Iron.
Meanwhile, the spiritual and biological factions represented by Cawl vehemently opposed them.
Some moderates continued to waver.
Guilliman had no doubt that, if the Men of Iron showed even the slightest willingness to accept the Adeptus Mechanicus, those red-robes with nothing but machine oil and knowledge in their heads would tear Mars in half without hesitation, then disregard their ancient pact with the Emperor and defect straight to the Men of Iron.
Fortunately, all the available information indicated that the Men of Iron had no affection whatsoever for these red-robed cosmic cockroaches. As long as they remained fanatically obsessed with ancient Federation technology, the Men of Iron would remain deeply averse to these deranged creatures.
Even mechanical beings did not want to be reduced to exhibits and teaching aids.
As for asking the Men of Iron to impart their knowledge?
The Adeptus Mechanicus probably possessed very few things of sufficient value to trade